This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A072983 #13 Apr 22 2025 02:44:52
%S A072983 1,2,6,6,30,5,35,35,35,70,770,770,10010,5005,15015,15015,255255,
%T A072983 255255,4849845,4849845,1616615,3233230,74364290,74364290,74364290,
%U A072983 37182145,37182145,37182145,1078282205,6469693230,200560490130,200560490130
%N A072983 Denominator of b(n) = Sum_{k'<=n} 1/k', where k' denotes the squarefree numbers.
%C A072983 b(n) was used by Niven in the 1970's for an alternative proof of the divergence of the sum of reciprocals of the primes.
%H A072983 Ivan Niven, <a href="http://www.jstor.org/stable/2317524">A Proof of the Divergence of sum 1/p</a>, The American Mathematical Monthly, Vol. 78, No. 3 (Mar., 1971), pp. 272-273.
%F A072983 a(n) = A354418(A013928(n+1)). - _Amiram Eldar_, Apr 22 2025
%t A072983 Accumulate[Table[If[SquareFreeQ[n], 1, 0]/n, {n, 1, 50}]] // Denominator (* _Amiram Eldar_, Apr 22 2025 *)
%o A072983 (PARI) a(n)=denominator(sum(k=1,n,issquarefree(k)/k))
%Y A072983 Cf. A005117, A013928, A072980 (numerators), A354418.
%K A072983 easy,frac,nonn
%O A072983 1,2
%A A072983 _Benoit Cloitre_, Aug 21 2002