A238900 Least k such that one of 2^n +- 2^k +- 1 is prime, where 0 < k < n, or 0 if there is no such prime.

1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 3, 1, 12, 2, 11, 1, 1, 1, 1, 2, 3, 9, 5, 2, 3, 3, 3, 4, 5, 4, 8, 3, 7, 4, 2, 6, 17, 14, 6, 12, 2, 5, 1, 2, 3, 6, 11, 5, 1, 16, 8, 8, 20, 2, 1, 5, 7, 19, 6, 4, 19, 8, 5, 4, 5, 3, 9, 6, 4, 3, 13, 1, 24

Offset: 2

Author

T. D. Noe, Mar 17 2014

Keywords

• nonn

Comments

Does a(n) = 0 for some n?

Links

• Giovanni Resta, Table of n, a(n) for n = 2..10000 (first 1999 terms from T. D. Noe)

Crossrefs

Cf. A196697.

Programs

Mathematica

Table[c1 = 2^n; k = 1; While[c2 = 2^k; k < n && ! (PrimeQ[c1 + c2 + 1] || PrimeQ[c1 + c2 - 1] || PrimeQ[c1 - c2 + 1] || PrimeQ[c1 - c2 - 1]), k++]; If[k == n, 0, k], {n, 2, 100}]