Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #9 Sep 26 2022 20:18:54
%S 30240,32760,2178540,23569920,45532800,46475520,48933360,50995620,
%T 60933600,69995520,72807696,142990848
%N Numbers k such that S(S(S(k))) = k, with S(n) = sigma(n)/4: 1/4-sociable numbers of order 1 or 3.
%C a(6..11) = { 46475520, 48933360, 50995620, ..., 72807696 } are the first terms not in A027687 (4-perfect numbers), which is obviously a subsequence.
%C a(11..12) = { 72807696, 142990848 } are the first terms that are not multiples of 60.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/SociableNumbers.html">Sociable Numbers</a>
%o (PARI) is_A355279(n, f(x)=if(x && x%4==0, sigma(x\4)))= f(f(sigma(n)))==n*4
%Y A027687 is a subsequence.
%Y Cf. A113286 (1/4 sociable numbers of order <= 2), A113546 (1/3-sociable numbers).
%K nonn,more
%O 1,1
%A _M. F. Hasler_, Sep 25 2022