OFFSET
1,1
COMMENTS
The sequence contains 12852 and 19751431167846, which are the smallest heptagonal numbers equal to twice another heptagonal number. - R. J. Mathar, Jan 13 2008
LINKS
Eric Weisstein's World of Mathematics, Heptagonal Number.
FORMULA
EXAMPLE
Where hep(k) = k-th heptagonal number = A000566(k):
a(1) = 697 = hep(17) = 616 + 81 = hep(16) + hep(6).
a(2) = 3186 = hep(36) = 1782 + 1404 = hep(27) + hep(24).
a(3) = 3744 = hep(39) = 2673 + 1071 = hep(33) + hep(21).
a(4) = 5221 = hep(46) = 4347 + 874 = hep(42) + hep(19).
MATHEMATICA
Module[{nn=1000, heps}, heps=Table[(n(5n-3))/2, {n, nn}]; Select[ Union[ Total/@ Tuples[Take[heps, nn/2], 2]], MemberQ[heps, #]&]] (* Harvey P. Dale, Dec 18 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Dec 19 2007
EXTENSIONS
More terms from R. J. Mathar, Jan 13 2008
STATUS
approved