A266143 Number of n-digit primes in which n-1 of the digits are 4's.

4, 3, 2, 2, 1, 2, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset

1,1

Comments

The leading digits must be 4's and only the trailing digit can vary.

For n large a(n) is usually zero.

Links

Michael De Vlieger and Robert G. Wilson v, Table of n, a(n) for n = 1..1500

Example

a(3) = 2 since 443 and 449 are primes.
a(4) = 2 since 4441 and 4447 are primes.

Mathematica

d = 4; Array[Length@ Select[d (10^# - 1)/9 + (Range[0, 9] - d), PrimeQ] &, 100]

Prog

(Python)
from __future__ import division
from sympy import isprime
def A266143(n):
    return 4 if n==1 else sum(1 for d in [-3, -1, 3, 5] if isprime(4*(10**n-1)//9+d)) # Chai Wah Wu, Dec 27 2015

Crossrefs

Cf. A265733, A266141, A266142, A266144, A266145, A266146, A266147, A266148, A266149, A099412, A096845, A099413, A099414.

Sequence in context: A347738 A082504 A237524 * A171623 A117462 A155462

Adjacent sequences: A266140 A266141 A266142 * A266144 A266145 A266146

Keyword

nonn,base

Author

Michael De Vlieger and Robert G. Wilson v, Dec 21 2015

Status

approved