OFFSET
1,9
COMMENTS
9 divides all terms, which shows the "casting out nines" congruence of multiplication.
LINKS
Indranil Ghosh, Rows 1..120 of triangle, flattened
Eric Weisstein's World of Mathematics, Casting Out Nines
Eric Weisstein's World of Mathematics, Digit Sum
Wikipedia, Digit sum
EXAMPLE
From Indranil Ghosh, Feb 14 2017: (Start)
Triangle:
1: 0,
2: 0, 0,
3: 0, 0, 0,
4: 0, 0, 9, 9,
5: 0, 9, 9, 18, 18,
6: 0, 9, 9, 18, 27, 27,
7: 0, 9, 18, 18, 27, 36, 36,
8: 0, 9, 18, 27, 36, 36, 45, 54,
9: 0, 9, 18, 27, 36, 45, 54, 63, 72,
10: 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
11: 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
12: 0, 0, 0, 0, 9, 9, 9, 9, 18, 0, 0, 0,
...
MATHEMATICA
dSum[n_] := Total[IntegerDigits[n]]; Flatten[Table[dSum[n]*dSum[k] - dSum[n*k], {n, 12}, {k, n}]] (* T. D. Noe, Oct 01 2013 *)
CROSSREFS
KEYWORD
AUTHOR
Enrique Pérez Herrero, Sep 28 2013
STATUS
approved