# Seriously disagreement

Artur grafix at csl.pl
Tue Sep 2 20:58:47 CEST 2008

```Dear Seqfans,
On www page
we can read that number of primes of the form 2x^2-1 for x equal or less
than 10^n is
8, 84, 815, 7922, 77250, 759077, 7492588, 74198995, 736401956,
7319543971, 72834161467
my result by Mathematica is
7,45,303,2202,17185,141444,1200975
disagreement of first position we can eliminated if we agree that 1 is
prime but what with rest ???
Best wishes
Artur

%S A143835 7,45,303,2202,17185,141444,1200975
%N A143835 a(n) = Number of n less or equal 10^n such than 2n^2-1 is prime
%e A143835 a(1)=7 because are 7 different n ={2, 3, 4, 6, 7, 8, 10}
equal or less than 10^1 where 2n^2-1 is prime = {7, 17, 31, 71, 97, 127,
199}
%t A143835 l = 0; p = 2; a = {}; Do[k = p x^2 - 1; If[PrimeQ[k], l = l +
1]; If[N[Log[x]/Log[10]] == Round[N[Log[x]/Log[10]]], Print[l];
AppendTo[a, l]], {x, 1, 10000000}]; a (*Artur Jasinski*)
%Y A143835 A066436, A066049, A090686, A090684, A143826, A143827,
A143828, A143829, A143830, A143831, A143832, A143833, A143834
%K A143835 base,nonn
%O A143835 1,1
%A A143835 Artur Jasinski (grafix(AT)csl.pl), Sep 02 2008

```