A117305 Triangular numbers for which the sum of the digits is a pentagonal number.

0, 1, 10, 66, 435, 561, 741, 903, 1128, 1326, 1830, 2145, 2415, 3081, 5151, 6105, 7140, 10731, 11325, 12090, 12720, 13530, 15051, 19110, 20910, 30135, 31125, 33411, 50403, 53301, 70500, 81003, 100128, 130305, 142311, 180300, 200028, 220116

Offset

1,3

Links

Table of n, a(n) for n=1..38.

Example

66 is in the sequence because (1) it is a triangular number and (2) the sum of its digits 6+6=12 is a pentagonal number.

Prog

(PARI) isok(n) = ispolygonal(n, 3) && ispolygonal(sumdigits(n), 5); \\ Michel Marcus, Feb 26 2014

Crossrefs

Cf. A000217, A000326.

Sequence in context: A163615 A232062 A229003 * A250790 A231886 A278090

Adjacent sequences: A117302 A117303 A117304 * A117306 A117307 A117308

Keyword

base,nonn

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 26 2006

Status

approved