OFFSET
1,1
EXAMPLE
a(2) = 12 as there are 12 2-digit primes whose digits are all odd: 11, 13, 17, 19, 31, 37, 53, 59, 71, 73, 79, 97.
MATHEMATICA
Length[Select[Prime[Range[PrimePi[10^(n - 1)], PrimePi[10^n]]], And @@ OddQ[IntegerDigits[#]] &]]
PROG
(Python)
from sympy import primerange
def a(n):
num=0
for f in range(1, 10, 2):
p=list(primerange(f*10**(n-1), (f+1)*10**(n-1)))
num+=sum(1 for k in p if all(int(d) %2 for d in str(k)))
return(num)
print ([a(n) for n in range(1, 8)])
(Python)
from sympy import isprime
from itertools import count, islice, product
def a(n):
c = 0 if n > 1 else 1
for p in product("13579", repeat=n-1):
s = "".join(p)
for last in "1379":
if isprime(int(s+last)): c += 1
return c
print([a(n) for n in range(1, 10)]) # Michael S. Branicky, Nov 27 2022
CROSSREFS
KEYWORD
base,nonn,more
AUTHOR
Zhining Yang, Nov 26 2022
EXTENSIONS
a(10)-a(14) from Michael S. Branicky, Nov 26 2022
a(15) from Zhining Yang, Dec 21 2022
a(16)-a(17) from Martin Ehrenstein, Dec 24 2022
STATUS
approved