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%I #12 Jan 08 2015 05:47:02
%S 6,66,325,210,1596,2701,1326,903,1225,16836,6903,82621,141778,181503,
%T 63546,52975,354903,10440,13530,405450,7140,989121,1329265,511566,
%U 668746,437580,2102275,2001000,2469753,3229611,1428895,3096316,1963171,6843150,856086,4276350
%N Difference of pairs of triangular numbers whose sum and difference are triangular.
%D Albert H. Beiler, Recreations in the theory of numbers, New York, Dover, (2nd ed.) 1966, p. 197, nr. 8.
%F a(n) = A185128(n) - A185129(n). - _Michel Marcus_, Jan 08 2015
%e a(2) = 66, since the pair of triangular numbers 171 = 18*(18+1)/2 and 105 = 14*(14+1)/2 produce the sum 276 = 23*(23+1)/2 and the difference 66 = 11*(11+1)/2 which are both triangular numbers.
%o (PARI) lista(nn) = {v = vector(nn, n, n*(n+1)/2); for (n=2, nn, for (k=1, n-1, if (ispolygonal(v[n]+v[k], 3) && ispolygonal(v[n]-v[k], 3), print1(v[n]-v[k], ", "));););} \\ _Michel Marcus_, Jan 08 2015
%Y Cf. A000217, A185128, A185129, A185223, A185233, A185243, A185257, A185258.
%K nonn
%O 1,1
%A _Martin Renner_, Jan 20 2012
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