OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
a(n) is the number whose base-3 representation is the base-2 representation of A235265(n).
MAPLE
f:= proc(n) local L, i;
L:= convert(n, base, 2);
isprime(add(L[i]*3^(i-1), i=1..nops(L)))
end proc:
select(f, [seq(ithprime(i), i=1..1000)]); # Robert Israel, Jun 03 2019
MATHEMATICA
Select[Prime@ Range@ 250, PrimeQ@ FromDigits[IntegerDigits[#, 2], 3] &] (* Michael De Vlieger, Jun 03 2019 *)
PROG
(PARI) is(p, b=3, c=2)=isprime(vector(#d=digits(p, c), i, b^(#d-i))*d~)&&isprime(p) \\ This code can be used for other bases b, c when b>c. See A235265 for code valid for b<c.
(PARI) forprime(p=2, 1e3, if(isprime(fromdigits(binary(p), 3)), print1(p", "))) \\ Charles R Greathouse IV, Mar 28 2022
(Python)
from sympy import isprime, nextprime
def agen(): # generator of terms
p = 2
while True:
p3 = sum(3**i for i, bi in enumerate(bin(p)[2:][::-1]) if bi=='1')
if isprime(p3):
yield p
p = nextprime(p)
g = agen()
print([next(g) for n in range(1, 65)]) # Michael S. Branicky, Jan 16 2022
CROSSREFS
KEYWORD
nonn,base
AUTHOR
M. F. Hasler, Jan 05 2014
STATUS
approved