A117052 Enneagonal numbers for which the product of the digits is also an enneagonal number.

0, 1, 9, 46, 111, 204, 750, 1089, 1350, 2301, 3075, 3504, 4200, 5500, 6069, 10071, 10450, 10836, 12036, 12450, 15081, 16014, 19500, 20026, 20559, 21099, 22200, 23904, 25075, 27501, 30039, 30691, 31350, 32016, 34056, 34750, 39061, 39804, 40554, 42075, 44409, 45201

Offset

1,3

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

46 is in the sequence because (1) it is an enneagonal number and (2) the product of its digits 4*6 = 24 is also an enneagonal number.

Mathematica

pod[n_] := Times @@ IntegerDigits[n]; ennQ[n_] := n == 0 || IntegerQ[(Sqrt[56*n + 25] + 5)/14]; Select[Table[n*(7*n - 5)/2, {n, 0, 120}], ennQ[pod[#]] &] (* Amiram Eldar, Feb 06 2021 *)

Crossrefs

Cf. A001106, A007954.

Sequence in context: A230062 A224851 A042003 * A356424 A280852 A009294

Adjacent sequences: A117049 A117050 A117051 * A117053 A117054 A117055

Keyword

base,nonn

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 15 2006

Extensions

Offset corrected by Amiram Eldar, Feb 06 2021

Status

approved