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A086072
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Number of 1's in decimal expansion of triangular number n(n+1)/2.
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9
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0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 1, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 2, 2, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 3, 1, 1, 2, 1, 1, 0, 1, 2, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0
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OFFSET
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0,19
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LINKS
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EXAMPLE
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tri(6)=21, so a(6)=1 and tri(1541)=1188111, so a(1541)=5.
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MATHEMATICA
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Table[DigitCount[(n(n+1))/2, 10, 1], {n, 0, 110}] (* Harvey P. Dale, Apr 24 2011 *)
DigitCount[#, 10, 1]&/@Accumulate[Range[0, 110]] (* Harvey P. Dale, Jun 25 2014 *)
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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