OFFSET
1,2
FORMULA
Values of k for which A024916(k)/k is an integer.
EXAMPLE
a(3) = 8 is in the sequence because A024916(8) / 8 = 56 / 8 = 7 is an integer. [Jaroslav Krizek, Dec 07 2009]
MAPLE
f := []: for i from 1 to 9000 do if add(sigma(n), n=1..i) mod i = 0 then f := [op(f), i] fi; od; f;
MATHEMATICA
k=10^4; a[1]=1; a[n_]:=a[n]=DivisorSigma[1, n]+a[n-1]; s=a/@Range@k; Select[Range@k, Divisible[s[[#]], #]&] (* Ivan N. Ianakiev, Apr 30 2016 *)
Module[{nn=44*10^5, ds}, ds=Accumulate[DivisorSigma[1, Range[nn]]]; Select[ Thread[{ds, Range[nn]}], Divisible[#[[1]], #[[2]]]&]][[All, 2]] (* The program generates the first 16 terms of the sequence. To generate more, increase the value of nn. *) (* Harvey P. Dale, Dec 04 2018 *)
PROG
(PARI) is(n)=sum(k=1, n, n\k*k)%n==0 \\ Charles R Greathouse IV, Feb 14 2013
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Asher Auel, Jun 06 2000
EXTENSIONS
More terms from Jud McCranie, Jul 04 2000
a(19)-a(24) from Donovan Johnson, Dec 29 2008
a(25) from Donovan Johnson, Jun 16 2011
a(26) from Jud McCranie, Dec 17 2024
a(27) from Jud McCranie, Dec 22 2024
a(28) from Jud McCranie, Apr 03 2025
a(29) from Jud McCranie, May 04 2025
STATUS
approved