OFFSET
1,1
COMMENTS
Besides a(1), is this sequence a subset of A091375? - Bill McEachen, Dec 18 2016
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
KEYWORD
easy,nonn,changed
AUTHOR
Omar E. Pol, May 16 2008
STATUS
approved