%I #4 Jun 30 2015 17:14:24
%S 3,6,10,15,10,6,10,15,21,28,36,45,36,28,36,45,55,36,21,28,36,45,36,28,
%T 36,45,55,66,78,91,78,66,78,91,105,78,55,66,78,91,78,66,78,91,105,120,
%U 136,153,120,78,91,105,91,78,66,78,105,120,136,153,171,153
%N (A259542(n) + A259542(n+1)) / 2.
%C All terms are triangular numbers by definition of A259542.
%H Reinhard Zumkeller, <a href="/A259604/b259604.txt">Table of n, a(n) for n = 1..10000</a>
%o (Haskell)
%o a259604 n = a259604_list !! (n-1)
%o a259604_list = zipWith ((flip div 2 .) . (+))
%o a259542_list $ tail a259542_list
%Y Cf. A259542, A000217, A086517, A259602, A259603, A259605.
%K nonn
%O 1,1
%A _Reinhard Zumkeller_, Jun 30 2015