A086072 Number of 1's in decimal expansion of triangular number n(n+1)/2.

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

Offset: 0

Author

Jason Earls, Jul 08 2003

Keywords

• base
• nonn

Examples

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

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.

Programs

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 *)