OFFSET
1,2
COMMENTS
Numbers k such that the number of divisors of k is equal to the number of divisors of k*(k+1)/2.
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = A045326(n) - 1. - Alois P. Heinz, Jan 27 2017
MAPLE
a:= proc(n) option remember; local p; p:= a(n-1)+2;
while irem(p, 4)<>3 do p:= nextprime(p) od; p-1
end: a(1):=1:
seq(a(n), n=1..100); # Alois P. Heinz, Jan 27 2017
MATHEMATICA
Select[Range@ 562, DivisorSigma[0, #] == DivisorSigma[0, PolygonalNumber@ #] &] (* Michael De Vlieger, Jan 27 2017, Version 10.4 *)
PROG
(PARI) select(n->numdiv(n)==numdiv(n*(n+1)/2), vector(1000, n, n))
CROSSREFS
KEYWORD
nonn
AUTHOR
Colin Barker, Jan 26 2017
STATUS
approved