A153238 Numbers k such that 2*k + 3 is composite.

3, 6, 9, 11, 12, 15, 16, 18, 21, 23, 24, 26, 27, 30, 31, 33, 36, 37, 39, 41, 42, 44, 45, 46, 48, 51, 54, 56, 57, 58, 59, 60, 61, 63, 65, 66, 69, 70, 71, 72, 75, 76, 78, 79, 81, 83, 84, 86, 87, 90, 91, 92, 93, 96, 99, 100, 101, 102, 103, 105, 106, 107, 108, 109, 111, 114

Offset: 1

Author

Vincenzo Librandi, Dec 21 2008

Keywords

• nonn
• easy

Comments

One less than the associated value in A047845. - R. J. Mathar, Jan 05 2011

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..10000
• Marc Wolf, François Wolf, Representation theorem of composite odd numbers indices, SCIREA Journal of Mathematics (2018) 3.3, 106-117.

Crossrefs

Cf. A067076, A047845, A144562.

Programs

Magma

[ n: n in [0..120] | not IsPrime(2*n+3) ]; // Klaus Brockhaus, Dec 19 2010

Mathematica

lst={};Do[If[ !PrimeQ[2*n+3],AppendTo[lst,n]],{n,6!}];lst (* Vladimir Joseph Stephan Orlovsky, Jan 10 2009 *)
Select[Range[120], CompositeQ[2 # + 3] &] (* Michael De Vlieger, Oct 17 2018 *)

PARI

for(n=1,115,if(!isprime(2*n+3),print1(n,", "))) \\ Joerg Arndt, Dec 19 2010

Formula

a(n) ~ n. - Charles R Greathouse IV, Dec 28 2011

Extensions

Edited by Ray Chandler, Jan 07 2009