A118749 Largest prime <= 3*n.

3, 5, 7, 11, 13, 17, 19, 23, 23, 29, 31, 31, 37, 41, 43, 47, 47, 53, 53, 59, 61, 61, 67, 71, 73, 73, 79, 83, 83, 89, 89, 89, 97, 101, 103, 107, 109, 113, 113, 113, 113, 113, 127, 131, 131, 137, 139, 139, 139, 149, 151, 151, 157, 157, 163, 167, 167, 173, 173, 179, 181

Offset: 1

Author

Jonathan Vos Post, Apr 29 2006

Keywords

• easy
• nonn

Comments

Analogous to A060308 largest prime <= 2*k.

Crossrefs

Cf. A007917 (largest prime <= n), A008585 (3n).

Cf. A060308, A118750, A118751, A118752.

Essentially the same as A081259.

Programs

Magma

[NthPrime(#PrimesUpTo(3*n)): n in [1..100]]; // Vincenzo Librandi, Nov 25 2015

Mathematica

Table[Max[FactorInteger[(3 n)!/(n!)^3]], {n, 1, 70}] (* Vincenzo Librandi, Nov 25 2015 *)
NextPrime[3*Range[70]+1,-1] (* Harvey P. Dale, Nov 12 2017 *)

PARI

vector(100, n, precprime(3*n)) \\ Altug Alkan, Nov 25 2015

Formula

a(n) = A007917(A008585(n)). - Michel Marcus, Nov 25 2015