

A301943


Number of primes of the form b^2+1 for b <= 10^n that end in 1.


2



1, 4, 42, 279, 2236, 18155, 152020, 1317648, 11634451, 104116591, 942191087
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OFFSET

1,2


LINKS

Table of n, a(n) for n=1..11.


FORMULA

a(n) + A301944(n) + 2 = A206709(n).


EXAMPLE

101, 401, 1601 and 8101 are primes; so a(2) = 4.


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 *)


PROG

(Python)
from sympy import isprime
def A301943(n):
return sum(1 for i in range(1, 10**(n1)+1) if isprime(100*i**2+1)) # Chai Wah Wu, Mar 30 2018


CROSSREFS

Cf. A002496, A206709, A301944.
Sequence in context: A220835 A157719 A280956 * A219101 A118447 A219980
Adjacent sequences: A301940 A301941 A301942 * A301944 A301945 A301946


KEYWORD

nonn,more,base


AUTHOR

Seiichi Manyama, Mar 29 2018


EXTENSIONS

a(10) from Robert G. Wilson v, Mar 31 2018
a(11) from Robert G. Wilson v, Apr 04 2018


STATUS

approved



