OFFSET
1,1
EXAMPLE
(2*1)^2 + 2*1 -1 = 5, (2*1)^2 + 2*1 +1 = 7, 5 and 7 twin primes so k(1)=2
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Jul 25 2005
STATUS
approved