OFFSET
1,2
COMMENTS
That is, numbers n, such that A166590(n) is divisible by n.
A000079, powers of 2, is a subsequence.
Thomas Ordowski remarks that the only squarefrees of this sequence are: 1, 2, 105, and 210.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..164
EXAMPLE
MATHEMATICA
a247213[n_] := Select[Range@n, Mod[Times @@ Power @@@ Transpose[{Plus[First /@ FactorInteger@#, 2], Last /@ FactorInteger@#}], #] == 0 &]; a247213[2^16] (* Michael De Vlieger, Jan 07 2015 *)
PROG
(PARI) isok(n) = { f = factor(n); for (i=1, #f~, f[i, 1] += 2); newn = factorback(f); newn % n == 0; }
(Python)
from operator import mul
from functools import reduce
from sympy import factorint
A247213_list = [n for n in range(1, 10**4) if n <= 1 or not reduce(mul, [(p+2)**e for p, e in factorint(n).items()]) % n]
# Chai Wah Wu, Jan 05 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, after a suggestion from Thomas Ordowski, Nov 26 2014
STATUS
approved