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A086073
Number of 2's in decimal expansion of triangular number n(n+1)/2.
9
0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0
OFFSET
0,50
EXAMPLE
tri(49)=1225, so a(49)=2 and tri(651)=212226, so a(651)=4.
MATHEMATICA
DigitCount[#, 10, 2]&/@Accumulate[Range[0, 120]] (* Harvey P. Dale, Jan 02 2016 *)
CROSSREFS
Cf. 0's A086071, 1's A086072, 3's A086074, 4's A086075, 5's A086076, 6's A086077, 7's A086078, 8's A086079, 9's A086080.
Sequence in context: A270668 A375051 A196272 * A053622 A016408 A316868
KEYWORD
base,nonn
AUTHOR
Jason Earls, Jul 08 2003
STATUS
approved