OFFSET
1,1
COMMENTS
Side lengths where both triangular numbers are the same (A053141) are not included. - R. J. Mathar, Feb 11 2018
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
R. J. Mathar, Table of n, a(n) for n = 1..58
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
A185128(2) = 171 which is the 18th triangular number, so a(2) = 18.
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(n, ", ")); ); ); } \\ Michel Marcus, Jan 08 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Martin Renner, Jan 20 2012
EXTENSIONS
Edited (with a simpler definition) by N. J. A. Sloane, Dec 28 2024
STATUS
approved