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 A185253 Difference of pairs of triangular numbers whose sum and difference are triangular. 7
 6, 66, 325, 210, 1596, 2701, 1326, 903, 1225, 16836, 6903, 82621, 141778, 181503, 63546, 52975, 354903, 10440, 13530, 405450, 7140, 989121, 1329265, 511566, 668746, 437580, 2102275, 2001000, 2469753, 3229611, 1428895, 3096316, 1963171, 6843150, 856086, 4276350 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES Albert H. Beiler, Recreations in the theory of numbers, New York, Dover, (2nd ed.) 1966, p. 197, nr. 8. LINKS FORMULA a(n) = A185128(n) - A185129(n). - Michel Marcus, Jan 08 2015 EXAMPLE 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. PROG (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 CROSSREFS Cf. A000217, A185128, A185129, A185223, A185233, A185243, A185257, A185258. Sequence in context: A119172 A064167 A175455 * A192089 A119073 A028559 Adjacent sequences:  A185250 A185251 A185252 * A185254 A185255 A185256 KEYWORD nonn AUTHOR Martin Renner, Jan 20 2012 STATUS approved

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Last modified June 12 13:18 EDT 2021. Contains 344947 sequences. (Running on oeis4.)