A117663 Heptagonal numbers for which the digital root is also a heptagonal number.

0, 1, 7, 34, 55, 235, 286, 403, 469, 874, 970, 1177, 1288, 1918, 2059, 2356, 2512, 3367, 3553, 3940, 4141, 5221, 5452, 5929, 6175, 7480, 7756, 8323, 8614, 10144, 10465, 11122, 11458, 13213, 13579, 14326, 14707, 16687, 17098, 17935, 18361, 20566, 21022, 21949

Offset

1,3

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (1,0,0,2,-2,0,0,-1,1).

Formula

G.f.: -x^2*(46*x^8+24*x^7+63*x^6+39*x^5+178*x^4+21*x^3+27*x^2+6*x+1) / ((x-1)^3*(x+1)^2*(x^2+1)^2). - Colin Barker, Jan 17 2014

Mathematica

drhQ[n_]:=MemberQ[{0, 1, 7}, NestWhile[Total[IntegerDigits[#]]&, n, #>9&]]; Select[ PolygonalNumber[ 7, Range[100]], drhQ] (* Harvey P. Dale, Mar 03 2024 *)

Crossrefs

Cf. A000566, A010888.

Sequence in context: A336277 A209897 A209814 * A063166 A259055 A195018

Adjacent sequences: A117660 A117661 A117662 * A117664 A117665 A117666

Keyword

nonn,base,easy

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 11 2006

Extensions

a(1)=0 inserted by Alois P. Heinz, Mar 16 2024

Status

approved