%I #9 May 26 2015 11:25:45
%S 0,1,3,21,171
%N Triangular numbers that are also Jacobsthal numbers (A001045).
%H Thomas Koshy and Zhenguang Gao, <a href="http://www.emis.de/journals/INTEGERS/papers/m64/m64.Abstract.html">Triangular Numbers in the Jacobsthal Family</a>, INTEGERS, Electronic J. of Combinatorial Number Theory, Vol. 12, Paper A64, 2012.
%Y Cf. A000217, A001045.
%K nonn,fini,full
%O 1,3
%A _Eric M. Schmidt_, Dec 04 2012