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

2,10

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)

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}]

Crossrefs

Cf. A196697.

Sequence in context: A091887 A144871 A066799 * A037832 A170977 A039737

Adjacent sequences: A238897 A238898 A238899 * A238901 A238902 A238903

Keyword

nonn

Author

T. D. Noe, Mar 17 2014

Status

approved