A152533 Numbers k>4 such that 10^k + 1111 is prime.

5, 11, 22, 41, 43, 203, 243, 305, 321, 570, 731, 1512, 1787, 2146, 3987, 4056, 5296

Offset

1,1

Comments

The decimal expansion of 10^k + 1111 consists of a single '1' digit followed by k-4 '0' digits followed by four '1' digits. (See Example section.)

a(18) > 40000. - Michael S. Branicky, Aug 07 2024

Links

Table of n, a(n) for n=1..17.

Example

101111 is prime, so 5 is in the sequence;
100000001111 is prime, so 11 is in the sequence.

Prog

(PARI) isok(n) = (n > 4) && isprime(10^n+1111); \\ Michel Marcus, Oct 15 2013
(Python)
from sympy import isprime, prime
def afind(limit, startk=5):
    k, pow10 = startk, 10**startk
    for k in range(startk, limit+1):
        if isprime(pow10 + 1111): print(k, end=", ")
        pow10 *= 10
afind(800) # Michael S. Branicky, Jan 22 2022

Crossrefs

Sequence in context: A024921 A189978 A192761 * A228485 A161896 A317909

Adjacent sequences: A152530 A152531 A152532 * A152534 A152535 A152536

Keyword

nonn,base,more

Author

Zak Seidov, Dec 06 2008

Extensions

Comments and example edited by Jon E. Schoenfield, Jan 14 2015

a(15)-a(17) from Michael S. Branicky, Jan 22 2022

Status

approved