A229767 - OEIS

%I #9 Jun 07 2022 15:20:44

%S 5,5,113,37,397,1613,61,953,457,14449,30269,8101,246241,107367629,

%T 384773,312709,47392381,184481113,1249,12112549,1759217765581,54001,

%U 140737471578113,4981857697937,26317,1801439824104653,415878438361,525313,174877,368140581013

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

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

%H Daniel Suteu, <a href="/A229767/b229767.txt">Table of n, a(n) for n = 1..547</a>

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

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

%Y Cf. A092440, A207262, A229747, A229768.

%K nonn

%O 1,1

%A _Colin Barker_, Sep 29 2013