This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
A123176[n] begin {2, 3, 4, 5, 6, 7, 8, 9, 11, 14, 18, 22, 26, 31, 39, 43, ...}.
Thus
a(1) = 2, a(2) = 3, a(3) = 5, a(4) = 7, a(5) = 11, a(6) = 31, a(7) = 43.
a(2)= 1398079: n=22: ((2^n-(-1)^n)/3-n)= 1398079, which is prime. a(4)= 393530540239137101071: n=70: ((2^n-(-1)^n)/3-n)= 393530540239137101071, which is prime.
KD := proc() local a; a:= (2^n -(-1)^n)/3-n; if isprime(a)then RETURN (a); fi; end: seq(KD(),n=1..1000);
for(n=8,500,if(ispseudoprime(t=2^n\/3-n),print1(t", "))) \\ Charles R Greathouse IV, Nov 13 2013
4 is in this sequence because (3^4 - (-2)^4)/5 = 13 is prime.
[n: n in [1..1000] | IsPrimePower((3^n-(-2)^n) div 5)];
Select[Range[2000], PrimeQ[(3^# - (-2)^#)/5] &] (* Michael De Vlieger, Dec 09 2017 *)
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