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 A185243 Sum of pairs of triangular numbers whose sum and difference are triangular. 7
 36, 276, 1081, 1770, 5886, 5671, 12246, 16653, 60031, 60726, 147153, 293761, 264628, 257403, 574056, 665281, 477753, 1345620, 1512930, 1450956, 2039190, 1695561, 1682695, 3454506, 3560446, 3932610, 2595781, 3589860, 3969153, 4258821, 8427565, 9003646, 12110581 (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) = 276, 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, A185253, A185257, A185258. Sequence in context: A220159 A202958 A187511 * A014136 A245435 A288963 Adjacent sequences:  A185240 A185241 A185242 * A185244 A185245 A185246 KEYWORD nonn AUTHOR Martin Renner, Jan 20 2012 STATUS approved

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Last modified February 28 11:08 EST 2020. Contains 332323 sequences. (Running on oeis4.)