A139270 Twice nonprime numbers.

2, 8, 12, 16, 18, 20, 24, 28, 30, 32, 36, 40, 42, 44, 48, 50, 52, 54, 56, 60, 64, 66, 68, 70, 72, 76, 78, 80, 84, 88, 90, 92, 96, 98, 100, 102, 104, 108, 110, 112, 114, 116, 120, 124, 126, 128, 130, 132, 136, 138, 140, 144, 148, 150

Offset

1,1

Comments

Besides a(1), is this sequence a subset of A091375? - Bill McEachen, Dec 18 2016

Links

Table of n, a(n) for n=1..54.

Formula

a(n) = A018252(n)*2.

Mathematica

2*Select[Range[75], !PrimeQ[#]&] (* Stefano Spezia, Nov 18 2023 *)

Prog

(PARI) is(n)=n%2==0 && !isprime(n/2) && n \\ Charles R Greathouse IV, Feb 21 2017
(Python)
from sympy import composite
def A139270(n): return composite(n-1)<<1 if n>1 else 2 # Chai Wah Wu, Oct 15 2024

Crossrefs

Cf. A018252.

Sequence in context: A276932 A340969 A180634 * A176100 A285658 A284802

Adjacent sequences: A139267 A139268 A139269 * A139271 A139272 A139273

Keyword

easy,nonn

Author

Omar E. Pol, May 16 2008

Status

approved