OFFSET
3,1
COMMENTS
The corresponding indices of n-gonal numbers are 3, 6, 12, 48, 51, 330, 1100, 702, ...
LINKS
Eric Weisstein's World of Mathematics, Polygonal Number
EXAMPLE
a(5) = 210, because 210 is a pentagonal number that has 5 pentagonal divisors {1, 5, 35, 70, 210} and this is the smallest such number.
PROG
(PARI) a(n) = if(n<3, return()); for(k=1, oo, my(t=(k*(n*k - n - 2*k + 4))\2); if(sumdiv(t, d, ispolygonal(d, n)) == n, return(t))); \\ Daniel Suteu, Dec 04 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 03 2022
EXTENSIONS
a(11)-a(25) from Daniel Suteu, Dec 04 2022
STATUS
approved