A221942 a(n) = floor(sqrt(5*2^n)).

2, 3, 4, 6, 8, 12, 17, 25, 35, 50, 71, 101, 143, 202, 286, 404, 572, 809, 1144, 1619, 2289, 3238, 4579, 6476, 9158, 12952, 18317, 25905, 36635, 51810, 73271, 103621, 146542, 207243, 293085, 414486, 586171, 828972, 1172343, 1657944, 2344687, 3315888, 4689374, 6631776, 9378748, 13263553, 18757497, 26527107

Offset: 0

Author

N. J. A. Sloane, Feb 01 2013

Keywords

• nonn

Comments

Theorem 3 of Dubickas implies that infinitely many terms of this sequence are divisible by 2 or 3 (and hence infinitely many composites). - Charles R Greathouse IV, Feb 04 2016

References

• Artūras Dubickas, Prime and composite integers close to powers of a number, Monatsh. Math. 158:3 (2009), pp. 271-284.

Links

• Harvey P. Dale, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A017910, A017913, A017919, A114183, A221718, A221942-A221946.

Programs

Mathematica

Floor[Sqrt[5*2^Range[0,50]]] (* Harvey P. Dale, Mar 09 2025 *)

PARI

a(n)=sqrtint(5*2^n) \\ Charles R Greathouse IV, Apr 18 2013