A139270 - OEIS

%I #21 Oct 15 2024 15:43:14

%S 2,8,12,16,18,20,24,28,30,32,36,40,42,44,48,50,52,54,56,60,64,66,68,

%T 70,72,76,78,80,84,88,90,92,96,98,100,102,104,108,110,112,114,116,120,

%U 124,126,128,130,132,136,138,140,144,148,150

%N Twice nonprime numbers.

%C Besides a(1), is this sequence a subset of A091375? - _Bill McEachen_, Dec 18 2016

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

%t 2*Select[Range[75],!PrimeQ[#]&] (* _Stefano Spezia_, Nov 18 2023 *)

%o (PARI) is(n)=n%2==0 && !isprime(n/2) && n \\ _Charles R Greathouse IV_, Feb 21 2017

%o (Python)

%o from sympy import composite

%o def A139270(n): return composite(n-1)<<1 if n>1 else 2 # _Chai Wah Wu_, Oct 15 2024

%Y Cf. A018252.

%K easy,nonn

%O 1,1

%A _Omar E. Pol_, May 16 2008