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 A064138 #21 Jun 02 2025 13:19:30
%S A064138 0,0,0,24,144,1398,11184,97200,973296,10950696,131408352,1593191808,
%T A064138 22304685312,333297226080,5103130001760,81686161277280,
%U A064138 1470350902991040,26490792085668288,529815841713365760,10635027891469974720
%N A064138 Sum of non-unitary divisors of n!.
%H A064138 Harry J. Smith, <a href="/A064138/b064138.txt">Table of n, a(n) for n = 1..100</a>
%F A064138 a(n) = sigma(n!) - usigma(n!) = A000203(n!) - A034448(A000142(n)) = A062569(n) - A034448(n!) = A048105(n!).
%e A064138 For n = 6, 6! = 720, the sum of its 30 divisors is 2418, the sum of the 8 unitary divisors is 1020, so the remaining 22 divisors give a(6) = 1398.
%t A064138 f1[p_, e_] := (p^(e + 1) - 1)/(p - 1); f2[p_, e_] := p^e + 1; a[n_] := Times @@ f1 @@@ (fct = FactorInteger[n!]) - Times @@ f2 @@@ fct; a[1] = 0; Array[a, 20] (* _Amiram Eldar_, Apr 01 2024 *)
%o A064138 (PARI) usigma(n)= { local(f,s=1); f=factor(n); for(i=1, matsize(f)[1], s*=1 + f[i, 1]^f[i, 2]); return(s) }
%o A064138 { n=0; f=1; for (n=1, 100, f*=n; write("b064138.txt", n, " ", sigma(f) - usigma(f)); ) } \\ _Harry J. Smith_, Sep 08 2009
%Y A064138 Cf. A034448, A048105, A046656, A056657, A056171, A056172, A000203, A000142, A062569, A063955, A063960.
%K A064138 nonn
%O A064138 1,4
%A A064138 _Labos Elemer_, Sep 11 2001
%E A064138 Term corrected and more terms added by _Harry J. Smith_, Sep 08 2009