%I #12 Jan 05 2025 19:51:41
%S 1,4,7,18
%N Lucas numbers that are also generalized heptagonal numbers.
%C Intersection of A000032 and A085787.
%C Except 4, these are also ordinary heptagonal numbers.
%C All terms are shown, as confirmed by Srinivasa Rao (2002).
%C All (generalized) g-gonal numbers in Lucas sequences up to g=20 have been determined, see Tengely (2009).
%H B. Srinivasa Rao, <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/Scanned/40-4/rao.pdf">Heptagonal Numbers in the Lucas Sequence and Diophantine Equations x^2(5x-3)^2 = 20y^2+-16</a>, The Fibonacci Quarterly, Vol. 40, No. 4 (2002), 319-322.
%H Szabolcs Tengely, <a href="http://shrek.unideb.hu/~tengely/G-gonal-FQ.pdf">Finding g-gonal numbers in recurrence sequences</a>, Fibonacci Quarterly, vol.46/47, no.3, pp.235-240, (2009).
%Y Cf. A000032, A085787.
%Y Cf. A248506 (triangular Lucas Numbers).
%K nonn,easy,full,fini
%O 1,2
%A _Tomohiro Yamada_, Sep 25 2017