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 A348651 #22 Oct 29 2021 04:57:14 %S A348651 1,1,1,4,29,293,2566,24844,259437,2908263,35102629,455204360, %T A348651 6321171774 %N A348651 Number of ones in the binary expansion of (n!)!. %H A348651 <a href="/index/Fa#factorial">Index entries for sequences related to factorial numbers</a> %F A348651 a(n) = A000120(A000197(n)). %e A348651 a(3) = 4 because (3!)! = 6! = 720 = 1011010000_2 which has 4 ones. %p A348651 a:= n-> add(i, i=Bits[Split](n!!)): %p A348651 seq(a(n), n=0..10); %t A348651 a[n_] := DigitCount[(n!)!, 2, 1]; Array[a, 10, 0] (* _Amiram Eldar_, Oct 29 2021 *) %o A348651 (Python) %o A348651 from gmpy2 import fac, popcount %o A348651 def A348651(n): return popcount(fac(fac(n))) # _Chai Wah Wu_, Oct 28 2021 %o A348651 (PARI) a(n) = hammingweight((n!)!); \\ _Michel Marcus_, Oct 29 2021 %Y A348651 Cf. A000120, A000142, A000197, A079584, A152168, A301861. %K A348651 nonn,base,more %O A348651 0,4 %A A348651 _Alois P. Heinz_, Oct 27 2021 %E A348651 a(11)-a(12) from _Chai Wah Wu_, Oct 28 2021