OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
{n : A001414(n) | (n-1)}. [R. J. Mathar, Aug 24 2010]
EXAMPLE
For example, 21=7x3, 7+3=10 which divides 21-1=20.
MAPLE
A001414 := proc(n) ifactors(n)[2] ; add( op(1, p)*op(2, p), p=%) ; end proc:
isA175729 := proc(n) if (n-1) mod A001414(n) = 0 then true; else false; end if; end proc:
for n from 2 to 10000 do if isA175729(n) then printf("%d, ", n) ; end if; end do:
# R. J. Mathar, Aug 24 2010
MATHEMATICA
fQ[n_] := Mod[n - 1, Plus @@ Flatten[ Table[ #1, {#2}] & @@@ FactorInteger@ n]] == 0; Select[ Range@ 6174, fQ] (* Robert G. Wilson v, Aug 25 2010 *)
PROG
(Magma) [k:k in [2..6200]| IsIntegral((k-1)/( &+[m[1]*m[2]: m in Factorization(k)]))]; // Marius A. Burtea, Sep 16 2019
(Python)
from sympy import factorint
def ok(n): return n>1 and (n-1)%sum(p*e for p, e in factorint(n).items())==0
print([k for k in range(10**4) if ok(k)]) # Michael S. Branicky, Sep 30 2022
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
K. T. Lee (7x3(AT)21cn.com), Aug 23 2010
EXTENSIONS
Extended by R. J. Mathar and Robert G. Wilson v, Aug 24 2010
STATUS
approved