A347694 Largest k <= 2*n such that k is a prime or twice a prime.

2, 4, 6, 7, 10, 11, 14, 14, 17, 19, 22, 23, 26, 26, 29, 31, 34, 34, 38, 38, 41, 43, 46, 47, 47, 47, 53, 53, 58, 59, 62, 62, 62, 67, 67, 71, 74, 74, 74, 79, 82, 83, 86, 86, 89, 89, 94, 94, 97, 97, 101, 103, 106, 107, 109, 109, 113, 113, 118, 118, 122, 122, 122, 127, 127, 131, 134, 134, 137, 139

Offset

1,1

Comments

Suggested by the formula for A016726.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

lkp2p[n_]:=Module[{k=2n}, While[NoneTrue[{k, k/2}, PrimeQ], k--]; k]; Array[lkp2p, 200] (* Harvey P. Dale, Mar 01 2025 *)

Crossrefs

Cf. A016726, A347693.

Sequence in context: A002158 A319829 A272631 * A274431 A236477 A189214

Adjacent sequences: A347691 A347692 A347693 * A347695 A347696 A347697

Keyword

nonn,changed

Author

N. J. A. Sloane, Oct 05 2021

Status

approved