OFFSET
1,1
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..1000
PROG
(PARI) isok(k) = if (isprime(k), my(d=Set(digits(k))); for (i=1, #d, if (!isprime(2*k*d[i]+1), return(0))); return(1)); \\ Michel Marcus, Mar 18 2025
(Python)
from gmpy2 import is_prime, digits
from itertools import count, product
def ok(n): return is_prime(n) and all(is_prime(2*n*d+1) for d in map(int, set(digits(n))))
def agen(): # generator of terms
yield from (k for d in count(1) for p in product("123456789", repeat=d-1) for e in "1379" if ok(int("".join(p)+e)))
print([k for k in range(10**7) if ok(k)]) # Michael S. Branicky, Nov 02 2025
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Michel Marcus, Mar 18 2025
STATUS
approved
