A097579 Triangular numbers k such that 2*k-1 is also a triangular number.

1, 28, 946, 32131, 1091503, 37078966, 1259593336, 42789094453, 1453569618061, 49378577919616, 1677418079648878, 56982836130142231, 1935739010345186971, 65758143515606214778, 2233841140520266115476, 75884840634173441711401

Offset

1,2

Links

Table of n, a(n) for n=1..16.

Index entries for linear recurrences with constant coefficients, signature (35, -35, 1).

Formula

G.f.: x*(1-7*x+x^2)/((1-x)*(1-34*x+x^2)).

Mathematica

CoefficientList[ Series[x*(1 - 7*x + x^2)/((1 - x)*(1 - 34*x + x^2)), {x, 0, 16}], x] (* Robert G. Wilson v, Sep 01 2004 *)
LinearRecurrence[{35, -35, 1}, {1, 28, 946}, 20] (* Harvey P. Dale, Aug 03 2025 *)

Crossrefs

Cf. A075528, A124174.

Sequence in context: A129461 A239336 A203135 * A091549 A034904 A189995

Adjacent sequences: A097576 A097577 A097578 * A097580 A097581 A097582

Keyword

easy,nonn

Author

Vladeta Jovovic, Aug 29 2004

Extensions

More terms from Robert G. Wilson v, Sep 01 2004

Status

approved