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 A358415 #11 Nov 15 2022 10:47:14 %S A358415 2,3,7,3,31,41,127,41,43,7,113,7,8191,6,6,313,131071,211457,524287,53, %T A358415 4217,433,41,547,2243,691921,21275809,673,76831,467,2147483647,89, %U A358415 112337,401,17681,9342799,12011,9511,19,1061129,164524721,5460123943,71,106661,33188053169,211,41 %N A358415 a(n) is the prime or perfect or amicable or sociable number encountered in the aliquot sequence for 2^n. %H A358415 Michel Marcus, <a href="/A358415/b358415.txt">Table of n, a(n) for n = 1..200</a> %H A358415 Jean-Luc Garambois, <a href="http://www.aliquotes.com/aliquotes_puissances_entieres/all/2.html">Aliquot sequences starting on integer powers 2^i</a> %F A358415 a(n) = A115350(2^n). %o A358415 (PARI) a(n) = my(b=2); if (n==1, return(b)); my(list = List(), s=b^n); for (i=1, oo, s = sigma(s) - s; if (#select(x->(x==s), list), return(s)); if (isprime(s), return (s)); listput(list, s);); %Y A358415 Cf. A001065, A115350, A358239, A358266. %K A358415 nonn %O A358415 1,1 %A A358415 _Michel Marcus_, Nov 14 2022