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A256480 Smallest prime obtained by appending n to a nonzero number with identical digits or 0 if no such prime exists. 2
0, 11, 0, 13, 0, 0, 0, 17, 0, 19, 0, 211, 0, 113, 0, 0, 0, 317, 0, 419, 0, 421, 0, 223, 0, 0, 0, 127, 0, 229, 0, 131, 0, 233, 0, 0, 0, 137, 0, 139, 0, 241, 0, 443, 0, 0, 0, 347, 0, 149, 0, 151, 0, 353, 0, 0, 0, 157, 0, 359, 0, 461, 0, 163, 0, 0, 0, 167, 0, 269 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
a(n) = 0 if n is even or a multiple of 5. Conjecture: all other terms are nonzero. Conjecture verified for n <= 10^7.
"Appending" means "on the right".
LINKS
PROG
(Python)
from gmpy2 import digits, mpz, is_prime
def A256480(n, limit=2000):
....sn = str(n)
....if not (n % 2 and n % 5):
........return 0
....for i in range(1, limit+1):
........for j in range(1, 10):
............si = digits(j, 10)*i
............p = mpz(si+sn)
............if is_prime(p):
................return int(p)
....else:
........return 'search limit reached.'
CROSSREFS
Sequence in context: A338827 A055963 A127805 * A088621 A088623 A167166
KEYWORD
nonn,base
AUTHOR
Chai Wah Wu, Mar 31 2015
STATUS
approved

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Last modified July 14 12:35 EDT 2024. Contains 374318 sequences. (Running on oeis4.)