A270102 Numbers k such that 3^k - k*2^k is prime.
3, 4, 5, 7, 8, 10, 11, 23, 34, 62, 95, 128, 173, 251, 260, 464, 628, 1267, 1895, 2057, 2743, 5102, 7790, 49163
Offset: 1
Examples
n = 4 is a term since 3^4 - 4*2^4 = 17 is prime.
Programs
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MATLAB
if isprime(3^n - n*2^n) disp(n) end
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Maple
A270102:=n->`if`(isprime(3^n-n*2^n),n,NULL): seq(A270102(n),n=1..2000); # Wesley Ivan Hurt, May 08 2016
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Mathematica
Select[Range[1, 1000], PrimeQ[3^# - #*2^#] &] (* Vaclav Kotesovec, Mar 11 2016 *)
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PARI
is(n)=ispseudoprime(3^n-n*2^n) \\ Charles R Greathouse IV, Jun 06 2017
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Python
from gmpy2 import is_prime for n in range(5000): if(is_prime(3**n-n*2**n)):print(n,end=", ") # Soumil Mandal, May 08 2016
Extensions
a(24) from Giovanni Resta, May 05 2016
Comments