A117650 Heptagonal numbers for which the sum of the digits is also a heptagonal number.

0, 1, 7, 34, 189, 403, 783, 1782, 2673, 3186, 3744, 4347, 6426, 7209, 8037, 8910, 10791, 11122, 12852, 13950, 15093, 16281, 17514, 21022, 21483, 24354, 27405, 30636, 32319, 34047, 35820, 39501, 41409, 43362, 45360, 47403, 51624, 53802, 56025

Offset

0,3

Links

Robert Israel, Table of n, a(n) for n = 0..10001

Example

196981 is in the sequence because it is a heptagonal number and the sum of its digits (34) is also a heptagonal number.

Maple

N:= 10000: # to search the first N heptagonal numbers
sd:= n -> convert(convert(n, base, 10), `+`):
hept:= x -> type((3+sqrt(9+40*x))/10, integer) or x = 0:
select(hept @ sd, [seq(n*(5*n-3)/2, n=0..N)]);
# Robert Israel, Feb 14 2013

Prog

(PARI) isok(n) = ispolygonal(n, 7) && ispolygonal(sumdigits(n), 7);
for(n=0, 1e5, if(isok(n), print1(n, ", "))) \\ Altug Alkan, Dec 08 2015

Crossrefs

Cf. A000566.

Sequence in context: A080048 A177140 A027233 * A365474 A273221 A144038

Adjacent sequences: A117647 A117648 A117649 * A117651 A117652 A117653

Keyword

nonn,base

Author

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

Extensions

a(0)=0 inserted by Georg Fischer, Mar 27 2024

Status

approved