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
Programs
-
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 *)
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