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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: A348004 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 May 29 18:36 EDT 2024. Contains 372952 sequences. (Running on oeis4.)