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A185233 Side of triangle of smaller member of a pair of triangular numbers whose sum and difference are triangular. 7
5, 14, 27, 39, 65, 54, 104, 125, 242, 209, 374, 459, 350, 275, 714, 782, 350, 1155, 1224, 1022, 1425, 840, 594, 1715, 1700, 1869, 702, 1260, 1224, 1014, 2645, 2430, 3185, 1127, 4094, 3317, 1274, 5124, 6060, 3834, 3059, 6174, 5565, 7749, 8349, 7395, 7344 (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

Table of n, a(n) for n=1..47.

EXAMPLE

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.

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(k, ", ")); ); ); } \\ Michel Marcus, Jan 08 2015

CROSSREFS

Cf. A000217, A185128, A185129, A185223, A185243, A185253, A185257, A185258.

Sequence in context: A080390 A030745 A071421 * A065351 A002503 A014106

Adjacent sequences:  A185230 A185231 A185232 * A185234 A185235 A185236

KEYWORD

nonn

AUTHOR

Martin Renner, Jan 20 2012

STATUS

approved

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Last modified December 11 18:34 EST 2019. Contains 329925 sequences. (Running on oeis4.)