OFFSET
1,2
COMMENTS
Numbers k such that the number of divisors of k is equal to the number of divisors of the pentagonal number k*(3*k-1)/2.
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
MATHEMATICA
Select[Range[500], DivisorSigma[0, #]==DivisorSigma[0, (#(3#-1))/2]&] (* Harvey P. Dale, Nov 12 2017 *)
PROG
(PARI) select(k->numdiv(k)==numdiv(k*(3*k-1)/2), vector(500, k, k))
CROSSREFS
KEYWORD
nonn
AUTHOR
Colin Barker, Jan 28 2017
STATUS
approved