OFFSET
1,2
COMMENTS
Intersection of A008587 and A000326. Their indices are given by A047215. - Michel Marcus, Feb 27 2014
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
Empirical G.f.: x^2*(5+30*x+25*x^2+15*x^3)/(1-x)^3/(1+x)^2. - Colin Barker, Feb 14 2012
a(2*n+1) = 5*n*(15*n-1)/2, a(2*n+2) = 5*(5*n+2)*(3*n+1)/2. - Robert Israel, Jun 01 2014
MATHEMATICA
Select[Table[PolygonalNumber[5, n], {n, 0, 100}], Divisible[#, 5] &] (* Amiram Eldar, Mar 22 2021 *)
Select[PolygonalNumber[5, Range[0, 200]], Mod[#, 5]==0&] (* Harvey P. Dale, Sep 08 2024 *)
PROG
(PARI) isok(n) = ispolygonal(n, 5) && !(n % 5); \\ Michel Marcus, Feb 27 2014
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Luc Stevens (lms022(AT)yahoo.com), Apr 29 2006
STATUS
approved