This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A111074 #6 Oct 31 2013 12:17:29
%S A111074 3,0,6,1,10,3,15,6,21,10,28,15,36,21,45,28,55,36,66,45,78,55,91,66,
%T A111074 105,78,120,91,136,105,153,120,171,136,190,153,210,171,231,190,253,
%U A111074 210,276,231,300,253,325,276,351,300,378,325,406,351,435,378,465,406,496,435
%N A111074 Let t(n) denote the triangular numbers (A000217). Sequence mixes t(n+2) and t(n).
%F A111074 G.f.: (3-3x+x^3)/((1-x)(1-x^2)^2); a(n)=a(n-1)+2a(n-2)-2a(n-3)-a(n-4)+a(n-5); - _Paul Barry_, Mar 22 2006
%t A111074 Flatten[ Table[{(n + 2)(n + 3)/2, n(n + 1)/2}, {n, 0, 29}]] (* _Robert G. Wilson v_ *)
%Y A111074 Cf. mix of t(n+1) and t(n): A008795.
%K A111074 easy,nonn
%O A111074 0,1
%A A111074 Stuart M. Ellerstein (ellerstein(AT)aol.com), Oct 10 2005
%E A111074 More terms from _Robert G. Wilson v_, Oct 11 2005