A138918 Numbers n such that 18n-1 is prime.

1, 3, 4, 5, 6, 10, 11, 13, 14, 15, 20, 24, 25, 26, 28, 29, 31, 33, 36, 38, 39, 40, 43, 45, 46, 48, 49, 53, 54, 59, 61, 64, 66, 68, 70, 71, 76, 80, 83, 84, 88, 89, 90, 91, 95, 104, 105, 106, 110, 111, 115, 116, 119, 123, 126, 130, 131, 133, 134, 136, 144, 145, 148, 150

Offset: 1

Author

Zak Seidov, Apr 03 2008

Keywords

• nonn
• easy

Comments

Corresponding primes are in A061242.

No terms in this sequence end with 2 or 7 (18n-1 ends with 5 when the last digit of n is 2 or 7). - David Garber, Jun 25 2015

Links

• Zak Seidov, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A061242, A258663.

Programs

Magma

[n: n in [0..150] | IsPrime(18*n-1)]; // Vincenzo Librandi, Jun 27 2015

Mathematica

Select[Range[200],PrimeQ[18#-1]&]  (* Harvey P. Dale, Mar 09 2011 *)

PARI

for(n=1,10^3,if(isprime(18*n-1),print1(n,", "))) \\ Derek Orr, Sep 03 2014

Python

from gmpy2 import divexact, t_mod
from sympy import prime
A138918 = [divexact(p+1,18) for p in (prime(n) for n in range(1,10**6)) if not t_mod(p+1,18)] # Chai Wah Wu, Sep 02 2014