1,2

The number of triangular numbers smaller than n can be found in sequence A002024 because n appears n times.

Table of n, a(n) for n=1..42.

2145 is in the sequence because (1) it is a triangular number, (2) the number of triangular numbers smaller than 2145 is 11 and (3) 2145 is divisible by 11.

Cf. A002024, A000217.

Sequence in context: A063525 A242454 A161777 * A091012 A241988 A058008

Adjacent sequences: A117516 A117517 A117518 * A117520 A117521 A117522

nonn

Luc Stevens (lms022(AT)yahoo.com), Apr 28 2006

approved