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 A382351 #6 Mar 29 2025 18:55:21 %S A382351 2,3,4,5,7,8,9,11,13,16,17,19,23,25,27,29,31,32,37,39,41,43,47,49,53, %T A382351 59,61,64,65,67,71,73,79,81,83,89,97,101,103,107,109,113,117,121,125, %U A382351 127,128,130,131,137,139,149,151,157,163,167,169,173,179,181,191,193,195,197,199,211 %N A382351 Numbers with an integer harmonic mean of the indices of distinct prime factors. %H A382351 <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>. %t A382351 Select[Range[2, 220], IntegerQ[HarmonicMean[PrimePi[#[[1]]] & /@ FactorInteger[#]]] &] %o A382351 (PARI) isok(k) = if (k>1, my(f=factor(k)); denominator(#f~/sum(i=1, #f~, 1/primepi(f[i,1]))) == 1); \\ _Michel Marcus_, Mar 22 2025 %Y A382351 Cf. A067340, A078174, A326621. %K A382351 nonn %O A382351 1,1 %A A382351 _Ilya Gutkovskiy_, Mar 22 2025