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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. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n=1..50.

EXAMPLE

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.

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:

CROSSREFS

Cf. A002496, A206400.

Sequence in context: A271552 A105510 A155951 * A254206 A118242 A006276

Adjacent sequences:  A208129 A208130 A208131 * A208133 A208134 A208135

KEYWORD

nonn

AUTHOR

Michel Lagneau, Oct 15 2012

STATUS

approved

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Last modified October 19 04:40 EDT 2019. Contains 328211 sequences. (Running on oeis4.)