OFFSET
1,2
COMMENTS
Conjecture: all elements of this sequence is greater than 0.
Conjecture tested hold up to n=2355. Further test is still running
The Mathematica program gives the first 100 terms.
Terms for all n are tend to be small integers.
4^n+/-4^k+/-1=2^2n+/-2^2k+/-1
EXAMPLE
n=1, 2=4^1-4^0-4^0, 1 prime found, so a(1)=1;
n=2, 11=4^2-4^1-1; 13=4^2-4^1+1; 19=4^2+4^1-1, 3 primes found, so a(2)=3;
...
n=13, 67043329=4^13-4^8+1; 67104769=4^13-4^6+1; 67108859=4^13-4^1-1; 67108879=4^13+4^2-1, 4 primes found, so a(13)=4;
MATHEMATICA
b = 4; Table[c1 = b^i; cs = {};
Do[c2 = b^j; cp = c1 + c2 + 1; If[PrimeQ[cp], cs = Union[cs, {cp}]];
cp = c1 + c2 - 1; If[PrimeQ[cp], cs = Union[cs, {cp}]];
cp = c1 - c2 + 1; If[PrimeQ[cp], cs = Union[cs, {cp}]];
cp = c1 - c2 - 1;
If[PrimeQ[cp], cs = Union[cs, {cp}]], {j, 0, i - 1}];
ct = Length[cs]; ct, {i, 1, 100}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Lei Zhou, Oct 06 2011
STATUS
approved