A117798 Icosagonal numbers divisible by 20.

0, 20, 820, 1200, 3440, 4180, 7860, 8960, 14080, 15540, 22100, 23920, 31920, 34100, 43540, 46080, 56960, 59860, 72180, 75440, 89200, 92820, 108020, 112000, 128640, 132980, 151060, 155760, 175280, 180340, 201300, 206720, 229120, 234900, 258740

Offset: 1

Author

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

Keywords

• easy
• nonn

Comments

Intersection of A008602 and A051872. - Michel Marcus, Feb 27 2014

Links

• Daniel Starodubtsev, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A008602, A051872.

Programs

Mathematica

Select[Table[PolygonalNumber[20, n], {n, 0, 200}], Divisible[#, 20] &] (* Amiram Eldar, Mar 22 2021 *)

PARI

isok(n) = ispolygonal(n, 20) && !(n % 20); \\ Michel Marcus, Feb 27 2014