A266145 Number of n-digit primes in which n-1 of the digits are 6's.
4, 2, 1, 1, 0, 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 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, 0
Offset: 1
Examples
a(2) = 2 since 61 and 67 are prime. a(3) = 1 since 661 is the only prime.
Links
- Michael De Vlieger and Robert G. Wilson v, Table of n, a(n) for n = 1..1500
Crossrefs
Programs
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Mathematica
d = 6; Array[Length@ Select[d (10^# - 1)/9 + (Range[0, 9] - d), PrimeQ] &, 100] Join[{4},Table[Count[Table[10FromDigits[PadRight[{},k,6]]+n,{n,{1,3,7,9}}], ?PrimeQ],{k,110}]] (* _Harvey P. Dale, Dec 23 2017 *) -
Python
from _future_ import division from sympy import isprime def A266145(n): return 4 if n==1 else sum(1 for d in [-5,-3,1,3] if isprime(2*(10**n-1)//3+d)) # Chai Wah Wu, Dec 27 2015
Comments