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 A332991 #11 Feb 16 2025 08:33:59 %S A332991 2,4,19,1307,266655247 %N A332991 a(n) is the smallest prime power p^k (p prime, k >= 1) such that sum of reciprocals of prime powers up to p^k (prime power harmonic sum) exceeds n. %C A332991 The corresponding indices of a(n) in A246655 are 1, 3, 12, 240, ... %H A332991 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PrimePower.html">Prime Power</a> %e A332991 a(1) = 4 because 1/2 + 1/3 = 0.8333... < 1 but 1/2 + 1/3 + 1/4 = 1.0833... > 1. %Y A332991 Similar sequences: A002387 (for positive integers), A016088 (for primes), A076751 (for composite numbers), A333004 (for squarefree numbers). %Y A332991 Cf. A246655 (prime powers). %K A332991 nonn,hard,more %O A332991 0,1 %A A332991 _Ilya Gutkovskiy_, Mar 05 2020 %E A332991 a(4) from _Daniel Suteu_, Mar 05 2020