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 Ramanujan-Nagell squares (8*(2^n - 1) + 1) and is therefore complete. - Raphie Frank, Sep 10 2012

Define equivalence classes on a specified real interval with respect to the symmetric transitive closure of R(x,y) = "x is an integer multiple of y". If any equivalence class is finite (the conditions for which are given in A328129), then a smallest equivalence class has cardinality 1, 2, 4 or 12. - Peter Munn, Jun 02 2021

LINKS

Eric Weisstein's World of Mathematics, Ramanujan's Square Equation

PROG

(PARI) is(n)=issquare(8<<n-7) \\ Charles R Greathouse IV, Sep 07 2012

CROSSREFS

KEYWORD

nonn,fini,full

AUTHOR

V. Raman, Aug 23 2012

EXTENSIONS

Four cross-references to the Ramanujan-Nagell problem added by Raphie Frank, Sep 10 2012

STATUS

approved