A296028 - OEIS

%I #51 Jan 29 2018 03:26:06

%S 0,1,0,1,1,0,0,1,1,0,0,1,1,0,0,1,0,0,0,1,1,0,0,0,1,0,0,1,1,0,0,1,0,0,

%T 0,1,0,0,0,1,1,0,0,0,1,0,0,1,1,0,0,0,1,0,0,1,0,0,0,1,0,0,0,0,1,0,0,1,

%U 1,0,0,1,1,0,0,1,0,0,0,0,0,0,0,0,1,0,0,1,0,0,0,1,1,0,0,0,0,0,0,1,1,0,0,0,1

%N Characteristic function of primes in the nonmultiples of 3.

%F From _David A. Corneth_, Dec 03 2017: (Start)

%F a(n) = A010051(A001651(n)).

%F a(n) = 1 if (6n - 3 - (-1)^n)/4 is prime, otherwise a(n) = 0. (End)

%e a(2) = 1 because the 2nd nonmultiple of 3 is 2, which is prime.

%p f:= n -> charfcn[{true}](isprime(floor((3*n-1)/2))):

%p map(f, [$1..1000]); # _Robert Israel_, Jan 24 2018

%t Array[Boole@ PrimeQ@ Floor[(3 # - 1)/2] &, 105] (* _Michael De Vlieger_, Dec 03 2017 *)

%o (PARI) a(n) = isprime(floor((3*n-1)/2)) \\ _Iain Fox_, Dec 03 2017

%o (PARI) first(n) = {my(inc = t = 1, res = vector(n)); for(i = 1, n, res[i] = isprime(t); t += inc; inc = 3-inc); res} \\ _David A. Corneth_, Dec 03 2017

%Y Cf. A001651, A010051, A045344.

%K nonn

%O 1

%A _Martin Michael Musatov_, Dec 03 2017