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 A036456 #33 Nov 28 2022 20:12:55 %S A036456 12,18,20,24,28,30,32,40,42,44,45,48,50,52,54,56,63,66,68,70,75,76,78, %T A036456 80,88,92,98,99,102,104,105,110,112,114,116,117,124,128,130,135,136, %U A036456 138,144,147,148,152,153,154,162,164,165,170,171,172,174,175,176,182 %N A036456 Numbers k for which exactly 4 applications of A000005 are needed to reach 2. %C A036456 Similar to but different from A007624. Terms like 60, 72, 84, 90, 96, 108, 126, etc. are not present here. %H A036456 Amiram Eldar, <a href="/A036456/b036456.txt">Table of n, a(n) for n = 1..10000</a> %F A036456 With d(n) = number of divisors(n), d(d(d(d(a(n))))) = 2 and d(d(d(a(n)))) > 2. %F A036456 A036459(a(n)) = 4. - _Ivan Neretin_, Jan 25 2016 %e A036456 a(3)=20 and a(17)=63; for both x=20 and 63, d(x)=6 and d(d(x))=4, the 3rd iterates are 3 and the equilibrium value, i.e., 2 appears as 4th iterates. %o A036456 (PARI) isok(n) = ((nd=numdiv(n)) != 2) && ((nd=numdiv(nd)) != 2) && ((nd=numdiv(nd)) != 2) && ((nd=numdiv(nd)) == 2); \\ _Michel Marcus_, Dec 30 2013 & Jan 26 2015 %Y A036456 Cf. A000005, A007624, A036450, A036452, A036453, A036455. %K A036456 nonn %O A036456 1,1 %A A036456 _Labos Elemer_ %E A036456 New name (using new name for A036457 from _Robert Israel_) from _Jon E. Schoenfield_, May 12 2018