A085649 Brilliant numbers k such that 2k+1 is also brilliant.

4, 10, 533, 671, 869, 1139, 2279, 14873, 17819, 20651, 22523, 23129, 23381, 25199, 28013, 28943, 31439, 31571, 33899, 35369, 35621, 37241, 37403, 39059, 39449, 41291, 42401, 42431, 42881, 43259, 45173, 45803, 49583, 49649, 49949, 50621

Offset: 1

Author

Jason Earls, Amarnath Murthy, Jul 11 2003

Keywords

• base
• nonn

Examples

			1139 is a member because 1139 = 17*67 and 1139*2+1 = 2279 = 43*53.
		

Crossrefs

Subsequence of A111153.

Cf. A078972.

Programs

PARI

isA078972(k)={my(f=factor(k));bigomega(f)==2 && (f[1,2]==2 || logint(f[1,1],10)==logint(f[2,1],10))}
isok(k)={isA078972(k) && isA078972(2*k+1)} \\ Andrew Howroyd, Sep 18 2024

Extensions

Offset changed by Andrew Howroyd, Sep 18 2024