A117832 - OEIS

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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

(list; graph; refs; listen; history; text; internal format)

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 an 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