A119529 Numbers k such that Sum_{j=1..k-1} j*2^(j-1) is prime.

3, 4, 8, 28, 52, 56, 82, 1472, 1484, 8669, 10886, 20804, 32606, 36392, 57005, 61628, 88652, 89732

Offset

1,1

Links

Table of n, a(n) for n=1..18.

Mathematica

s = 0; Do[s += (x-1)*2^(x-1)/2; If[PrimeQ[s], Print[x]], {x, 10^4}] (* Ryan Propper, Jan 01 2007 *)
Select[Range[1, 2000], PrimeQ[2^(#-1)*(#-2) + 1] &] (* Vaclav Kotesovec, Jul 01 2024 *)

Crossrefs

Cf. A000523, A125569.

Sequence in context: A168382 A155701 A353950 * A366812 A180629 A258372

Adjacent sequences: A119526 A119527 A119528 * A119530 A119531 A119532

Keyword

nonn,more

Author

Jorge Coveiro, Jul 27 2006

Extensions

a(10) from Ryan Propper, Jan 01 2007

Name simplified by Jon E. Schoenfield, Sep 23 2018

a(11)-a(14) from Amiram Eldar, Dec 01 2021

a(15)-a(16) from Michael S. Branicky, May 04 2023

a(17)-a(18) from Michael S. Branicky, Jun 30 2024

Status

approved