OFFSET
0,19
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
KEYWORD
base,nonn
AUTHOR
Jason Earls, Jul 08 2003
STATUS
approved