A270102 - OEIS

%I #31 Oct 14 2024 00:03:20

%S 3,4,5,7,8,10,11,23,34,62,95,128,173,251,260,464,628,1267,1895,2057,

%T 2743,5102,7790,49163

%N Numbers n such that 3^n - n*2^n is prime.

%C a(25) > 10^5. - _Michael S. Branicky_, Oct 13 2024

%e n = 4 is a term since 3^4 - 4*2^4 = 17 is prime.

%p A270102:=n->`if`(isprime(3^n-n*2^n),n,NULL): seq(A270102(n),n=1..2000); # _Wesley Ivan Hurt_, May 08 2016

%t Select[Range[1, 1000], PrimeQ[3^# - #*2^#] &] (* _Vaclav Kotesovec_, Mar 11 2016 *)

%o (MATLAB)

%o if isprime(3^n - n*2^n)

%o disp(n)

%o end

%o (Python)

%o from gmpy2 import is_prime

%o for n in range(5000):

%o    if(is_prime(3**n-n*2**n)):print(n,end=", ")

%o # _Soumil Mandal_, May 08 2016

%o (PARI) is(n)=ispseudoprime(3^n-n*2^n) \\ _Charles R Greathouse IV_, Jun 06 2017

%Y Cf. A057468, A270104.

%K nonn,more,changed

%O 1,1

%A _Vardan Semerjyan_, Mar 11 2016

%E a(24) from _Giovanni Resta_, May 05 2016