A098268 Unique prime factors of 2^n+1 are of the form kn+1. These are the values for k.

2, 2, 0, 4, 2, 2, 6, 32, 2, 4, 62, 20, 210, 2, 8, 22, 4096, 2570, 2, 6, 9198, 3084, 258, 18, 96, 121574, 4, 28, 10, 162, 2, 6, 62, 3230, 563940, 2, 104592, 2, 44, 23091222

Offset: 1

Author

Marco Matosic, Sep 01 2004

Keywords

• nonn

Comments

The values for 2^n+1 are in A000051. In this sequence where a(n) has more than one k value they are separated with commas. See A097406 & A097407.

Programs

PARI

isprimitivep(p, n) = {for (r=1, n-1, if (((2^r+1) % p) == 0, return (0));); return (1);}
lista(n) = {f = factor(2^n+1); hasprim = 0;for(i=1, #f~, if (isprimitivep(f[i, 1], n), hasprim = 1; print1((f[i, 1]-1)/n, ", "););); if (! hasprim, print1(0, ", "));} \\ Michel Marcus, Jul 16 2013