A208132 Smallest k such that the number of composites of the form a^2 + 1 between two successive primes of this form equals 2n-1.

2, 4, 17, 15, 10, 26, 12, 19, 112, 34, 163, 91, 101, 135, 303, 97, 54, 229, 459, 70, 679, 1075, 340, 1041, 550, 836, 1308, 2780, 606, 875, 4057, 2398, 772, 1891, 1065, 3900, 2610, 8065, 7476, 4161, 6023, 5815, 1481, 351, 5385, 16978, 3410, 19756, 16044, 3309

Offset: 1

Author

Michel Lagneau, Oct 15 2012

Keywords

• nonn

Comments

Smallest k such that A206400(k) = 2n-1.

Examples

			a(4) = 15 because A206400(15) = 7 = 2*4 - 1. There are 7 composites of the form a^2+ 1 between the two primes 66^2+1 = 4357 and 74^2+1 = 5477.
		

Crossrefs

Cf. A002496, A206400.

Programs

Maple

n0:=500000:T:=array(1..n0):j:=0:i:=0:for m from 2 to n0 do:x:=m^2+1:if type (x, prime)=true then j:=j+1:T[j]:=i:i:=0:else i:=i+1:fi:od: for n from 1 to 50 do:ii:=0:for k from 1 to j while(ii=0) do:if T[k]=2*n-1 then ii:=1: printf(`%d, `,k):else fi:od:od: