A117793 Pentagonal numbers divisible by 5.

0, 5, 35, 70, 145, 210, 330, 425, 590, 715, 925, 1080, 1335, 1520, 1820, 2035, 2380, 2625, 3015, 3290, 3725, 4030, 4510, 4845, 5370, 5735, 6305, 6700, 7315, 7740, 8400, 8855, 9560, 10045, 10795, 11310, 12105, 12650, 13490, 14065, 14950, 15555, 16485

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 *)

Prog

(PARI) isok(n) = ispolygonal(n, 5) && !(n % 5); \\ Michel Marcus, Feb 27 2014

Crossrefs

Cf. A000326, A008587, A047215.

Sequence in context: A117985 A371561 A115707 * A145920 A356179 A356132

Adjacent sequences: A117790 A117791 A117792 * A117794 A117795 A117796

Keyword

easy,nonn

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 29 2006

Status

approved