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%I #15 Jan 08 2015 05:46:52
%S 5,14,27,39,65,54,104,125,242,209,374,459,350,275,714,782,350,1155,
%T 1224,1022,1425,840,594,1715,1700,1869,702,1260,1224,1014,2645,2430,
%U 3185,1127,4094,3317,1274,5124,6060,3834,3059,6174,5565,7749,8349,7395,7344
%N Side of triangle of smaller member of a pair 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.
%e a(2) = 14, 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(k, ", "));););} \\ _Michel Marcus_, Jan 08 2015
%Y Cf. A000217, A185128, A185129, A185223, A185243, A185253, A185257, A185258.
%K nonn
%O 1,1
%A _Martin Renner_, Jan 20 2012
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