OFFSET
1,3
EXAMPLE
2*3*2^0-1=5, 2*3*2^0+1=7 twin prime of 5 so a(1)=0
2*3*2^1-1=11, 2*3*2^1+1=13 twin prime of 11 so a(2)=1
2*3*2^2-1=23 prime but not twin prime
2*3*2^3-1=47 prime but not twin prime
2*3*2^4-1=95 composite
2*3*5*2^4-1=479 prime but not twin prime
2*3*2^5-1=191, 2*3*2^5+1=193 twin prime of 191 so a(3)=5
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Dec 09 2010
STATUS
approved