

A215795


Numbers n such that 2^n1 is a triangular number (A000217).


5




OFFSET

1,3


COMMENTS

Aside from a(2), all terms are even. Probably complete; no more terms up to 10^6.  Charles R Greathouse IV, Sep 07 2012
This sequence maps to the RamanujanNagell squares (8*(2^n  1) + 1) and is therefore complete.  Raphie Frank, Sep 10 2012


LINKS

Table of n, a(n) for n=1..5.
Eric Weisstein's World of Mathematics, Ramanujan's Square Equation


PROG

(PARI) is(n)=issquare(8<<n7) \\ Charles R Greathouse IV, Sep 07 2012


CROSSREFS

Cf. A000217, A060728, A038198.
Cf. A076046 (triangular numbers of the form 2^n  1).
Cf. A060728 (a(n) + 3).
Cf. A038198 (sqrt(8*(2^n  1)+1)).
Cf. A215797 ((sqrt(8*(2^n  1)+1)  1)/2).
Sequence in context: A227530 A218129 A156519 * A070314 A075554 A294103
Adjacent sequences: A215792 A215793 A215794 * A215796 A215797 A215798


KEYWORD

nonn,fini,full


AUTHOR

V. Raman, Aug 23 2012


EXTENSIONS

Four crossreferences to the RamanujanNagell problem added by Raphie Frank, Sep 10 2012


STATUS

approved



