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A187885 Numbers n such that n*p + 1 is a square for some prime p. 0
1, 3, 4, 5, 7, 8, 9, 11, 12, 13, 15, 16, 17, 19, 21, 24, 25, 27, 29, 31, 32, 33, 35, 39, 40, 41, 43, 45, 48, 49, 51, 55, 56, 57, 59, 60, 61, 63, 64, 65, 69, 71, 72, 73, 75, 77, 80, 81, 84, 85, 87, 88, 91, 93, 95, 96, 99, 101, 103, 104, 105, 107, 109, 111, 112, 115, 120 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The smallest corresponding p are {3, 5, 2, 3, 5, 3, 7, 13, 2, 11, 13, 3, 19, 17, 3, 2, 23, 29, 31, 29, 7, 3, 37,...}

LINKS

Table of n, a(n) for n=1..67.

FORMULA

Complement of A187884.

EXAMPLE

21 is in the sequence because 21*3 + 1 = 8^2, with p = 3.

MAPLE

with(numtheory): for k from 1 to 120 do : q:=0:for p from 1 to 200 do : x:=sqrt(k*p+1)

  : if x=trunc(x) and type(p, prime)=true and q=0 then q:=1: printf(`%d, `, k):else

  fi:od:od:

CROSSREFS

Cf. A187884, A187886.

Sequence in context: A042965 A260003 A005848 * A039065 A247786 A330565

Adjacent sequences:  A187882 A187883 A187884 * A187886 A187887 A187888

KEYWORD

nonn

AUTHOR

Michel Lagneau, Mar 15 2011

STATUS

approved

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Last modified February 20 15:52 EST 2020. Contains 332078 sequences. (Running on oeis4.)