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 A333004 #9 Feb 16 2025 08:33:59 %S A333004 1,2,5,26,130,670,3466,17985,93179,482762,2501013,12956855,67125243, %T A333004 347753857,1801596939 %N A333004 a(n) is the smallest squarefree number k such that sum of reciprocals of squarefree numbers up to k (squarefree harmonic sum) exceeds n. %C A333004 The corresponding indices of a(n) in A005117 are 1, 2, 4, 17, 80, 409, 2112, 10936, 56651, 293483, 1520429, ... %H A333004 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Squarefree.html">Squarefree</a> %e A333004 a(2) = 5 because 1/1 + 1/2 + 1/3 = 1.8333... < 2 but 1/1 + 1/2 + 1/3 + 1/5 = 2.0333... > 2. %Y A333004 Similar sequences: A002387 (for positive integers), A016088 (for primes), A076751 (for composite numbers), A332991 (for prime powers). %Y A333004 Cf. A005117 (squarefree numbers). %K A333004 nonn,hard,more %O A333004 0,2 %A A333004 _Ilya Gutkovskiy_, Mar 05 2020 %E A333004 a(11)-a(14) from _Daniel Suteu_, Mar 05 2020