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Table of n, a(n) for n=1..15.
Eric Weisstein's World of Mathematics, Triangular Number
Sequence in context: A167533 A244907 A062477 * A231215 A231340 A099321
Adjacent sequences: A048359 A048360 A048361 * A048363 A048364 A048365
Patrick De Geest, Mar 15 1999.
a(13)-a(15) from Lars Blomberg, May 16 2011