|
%I #8 Jun 30 2015 13:22:36
%S 7,45,303,2202,17185,141444,1200975,10448345,92435171,828797351,
%T 7511268020,68680339342
%N a(n) = Number of x <= 10^n such that 2x^2-1 is prime.
%H Bernhard Helmes, <a href="http://www.devalco.de/quadr_Sieb_2x%5E2-1.php#4a">Prime sieving on the polynomial f(n)=2n^2-1</a>.
%e a(1) = 7 because are 7 different x ={2, 3, 4, 6, 7, 8, 10} <= 10^1 where 2x^2-1 is prime = {7, 17, 31, 71, 97, 127, 199}.
%t 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 Cf. A066436, A066049, A090686, A090684, A143826, A143827, A143828, A143829, A143830, A143831, A143832, A143833, A143834.
%K nonn
%O 1,1
%A _Artur Jasinski_, Sep 02 2008, Sep 04 2008
%E Added link and extended to agree with website. - _Ray Chandler_, Jun 30 2015
|
