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 A107914 #14 Mar 18 2024 03:27:22
%S A107914 81,1681,3481,5041,7921,17161,27889,29929,83521,146689,279841,491401,
%T A107914 552049,579121,635209,683929,703921,707281,829921,1190281,1203409,
%U A107914 1352569,1481089,1885129,2036329,2211169,2430481,2505889,3279721,3411409,3523129,3568321,3728761
%N A107914 Numbers k that require four iterations of the sigma function to be >= 2*k.
%C A107914 Most of the early terms are the square of a prime or the fourth power of a prime.
%H A107914 Amiram Eldar, <a href="/A107914/b107914.txt">Table of n, a(n) for n = 1..500</a>
%e A107914 sigma(sigma(sigma(81))) = 160 but sigma(sigma(sigma(sigma(81)))) = 378, so 81 is in the sequence.
%o A107914 (PARI) is(n) = {my(m = n, nn = 2*n, c = 0); while(m < nn, m = sigma(m); c++); c == 4;} \\ _Amiram Eldar_, Mar 18 2024
%Y A107914 Cf. A000203, A055020, A055021, A107912, A107913.
%K A107914 nonn
%O A107914 1,1
%A A107914 _Jud McCranie_, May 27 2005
%E A107914 Offset 1 by _Michel Marcus_, Apr 25 2020
%E A107914 More terms from _Amiram Eldar_, Mar 18 2024