A229767 Largest prime factor of 2^(2*n+1)-2^(n+1)+1.

5, 5, 113, 37, 397, 1613, 61, 953, 457, 14449, 30269, 8101, 246241, 107367629, 384773, 312709, 47392381, 184481113, 1249, 12112549, 1759217765581, 54001, 140737471578113, 4981857697937, 26317, 1801439824104653, 415878438361, 525313, 174877, 368140581013

Offset: 1

Author

Colin Barker, Sep 29 2013

Keywords

• nonn

Comments

2^(2*n+1)-2^(n+1)+1 is a factor of 4^(2*n+1)+1.

Examples

			For n=5, 2^(2*n+1)-2^(n+1)+1 = 1985 = 5*397, so a(5)=397.
		

Links

• Daniel Suteu, Table of n, a(n) for n = 1..547

Crossrefs

Cf. A092440, A207262, A229747, A229768.

Programs

PARI

a(n) = {f=factor(2^(2*n+1)-2^(n+1)+1); f[matsize(f)[1],1]}