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A086072 Number of 1's in decimal expansion of triangular number n(n+1)/2. 9
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,19

LINKS

Table of n, a(n) for n=0..104.

EXAMPLE

tri(6)=21, so a(6)=1 and tri(1541)=1188111, so a(1541)=5.

MATHEMATICA

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 *)

CROSSREFS

Cf. 0's A086071, 2's A086073, 3's A086074, 4's A086075, 5's A086076, 6's A086077, 7's A086078, 8's A086079, 9's A086080.

Sequence in context: A127327 A321144 A309048 * A086009 A086010 A321929

Adjacent sequences:  A086069 A086070 A086071 * A086073 A086074 A086075

KEYWORD

base,nonn

AUTHOR

Jason Earls, Jul 08 2003

STATUS

approved

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Last modified October 24 16:24 EDT 2021. Contains 348233 sequences. (Running on oeis4.)