OFFSET
1,4
LINKS
Harry J. Smith, Table of n, a(n) for n = 1..100
FORMULA
EXAMPLE
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.
MATHEMATICA
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 *)
PROG
(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) }
{ n=0; f=1; for (n=1, 100, f*=n; write("b064138.txt", n, " ", sigma(f) - usigma(f)); ) } \\ Harry J. Smith, Sep 08 2009
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 11 2001
EXTENSIONS
Term corrected and more terms added by Harry J. Smith, Sep 08 2009
STATUS
approved