A117832 Triangular numbers for which the product of the digits is an octagonal number.

0, 1, 10, 105, 120, 190, 210, 300, 406, 595, 630, 703, 780, 820, 903, 990, 1035, 1081, 1540, 1770, 1830, 2016, 2080, 2145, 2415, 2701, 2850, 3003, 3081, 3160, 3240, 3403, 3570, 4005, 4095, 4560, 4950, 5050, 5460, 6105, 6441, 6670, 6903, 7021, 7140, 7260

Offset

1,3

Links

Table of n, a(n) for n=1..46.

Example

595 is in the sequence because (1) it is a triangular number and (2) the product of its digits 5*9*5=225 is a octagonal number.

Mathematica

Select[Accumulate[Range[0, 200]], DigitCount[#, 10, 0]>0||IntegerQ[(1+ Sqrt[ 1+3*Times@@ IntegerDigits[ #]])/3]&] (* Harvey P. Dale, Jul 24 2016 *)

Crossrefs

Cf. A000217, A000567.

Sequence in context: A110957 A077671 A117833 * A268763 A300850 A360276

Adjacent sequences: A117829 A117830 A117831 * A117833 A117834 A117835

Keyword

base,nonn

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 30 2006

Extensions

Corrected by Harvey P. Dale, Jul 24 2016

Status

approved