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A117663
Heptagonal numbers for which the digital root is also a heptagonal number.
1
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
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
Sequence in context: A336277 A209897 A209814 * A063166 A259055 A195018
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