A185233 A185129(n) is the a(n)-th triangular number.

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

Offset

1,1

Comments

See A185128 for further information.

References

Albert H. Beiler, Recreations in the theory of numbers, New York, Dover, (2nd ed.) 1966, p. 197, no. 8.

Links

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

N. J. A. Sloane, Annotated scan of Beiler's Table 81, based on page 197 of Beiler's "Recreations in the Theory of Numbers: The Queen of Mathematics Entertains", New York, Dover, First ed., 1964.

Example

A185122(2) = 105 which is the 14th triangular number, so a(2) = 14.

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 A375291

Adjacent sequences: A185230 A185231 A185232 * A185234 A185235 A185236

Keyword

nonn

Author

Martin Renner, Jan 20 2012

Extensions

Edited (with a simpller definition) by N. J. A. Sloane, Dec 28 2024

Status

approved