A301943 Number of primes of the form b^2+1 for b <= 10^n that end in 1.
1, 4, 42, 279, 2236, 18155, 152020, 1317648, 11634451, 104116591, 942191087
Offset: 1
Examples
101, 401, 1601 and 8101 are primes; so a(2) = 4.
Programs
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Mathematica
c = k = 0; lst = {}; Do[ While[k <= 10^n, If[ PrimeQ[k^2 + 1], c++]; k+=10]; AppendTo[lst, c]; Print[c], {n, 9}] (* Robert G. Wilson v, Mar 30 2018 *) -
Python
from sympy import isprime def A301943(n): return sum(1 for i in range(1,10**(n-1)+1) if isprime(100*i**2+1)) # Chai Wah Wu, Mar 30 2018
Extensions
a(10) from Robert G. Wilson v, Mar 31 2018
a(11) from Robert G. Wilson v, Apr 04 2018