A210733 Least k > n-1 such that 4^n + 2^k - 1 is a prime number.
1, 2, 3, 4, 6, 6, 12, 9, 10, 10, 27, 13, 15, 22, 16, 16, 18, 19, 39, 22, 22, 43, 24, 24, 48, 26, 28, 43, 32, 38, 75, 33, 36, 58, 35, 57, 55, 47, 48, 52, 54, 72, 52, 51, 72, 54, 72, 53, 64, 62, 52, 52, 63, 60, 55, 60, 316, 70, 63, 68, 64, 96, 66, 115, 66, 92
Offset: 1
Keywords
Examples
4^1+2^1-1=5 prime so a(1)=1. 4^2+2^2-1=19 prime so a(2)=2. 4^3+2^3-1=71 prime so a(3)=3.
Links
- Pierre CAMI, Table of n, a(n) for n = 1..3867
Programs
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Mathematica
Table[k = n; While[! PrimeQ[4^n + 2^k - 1], k++]; k, {n, 100}] (* T. D. Noe, May 16 2012 *)
Extensions
Missing a(2103) inserted into b-file by Andrew Howroyd, Feb 24 2018
Comments