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A138685 Numbers n such that there is no prime of the form 2n + p^2 for any prime p. 10
13, 28, 34, 43, 55, 58, 67, 73, 76, 88, 97, 100, 103, 106, 118, 133, 139, 145, 148, 157, 160, 163, 166, 178, 181, 184, 193, 199, 202, 208, 214, 223, 232, 238, 244, 253, 259, 262, 265, 268, 271, 283, 286, 298, 301, 307, 310, 313, 328, 331, 340, 343, 349, 352 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Indices where zero occurs in A138479.

For primes in this sequences see A138686.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

FORMULA

Based on comments from Zak Seidov, Don Reble and M. F. Hasler, we now know that these are the numbers n such that n == 1 (mod 3) and 2n + 9 is composite. - N. J. A. Sloane, Apr 20 2008

MATHEMATICA

a = {}; Do[p = 0; While[(! PrimeQ[2*n + Prime[p + 1]^2]) && (p < 10000), p++ ]; If[p < 10000, [null], AppendTo[a, n]], {n, 1, 550}]; a

Select[Range[400], Mod[#, 3]==1&&CompositeQ[2#+9]&] (* Harvey P. Dale, Feb 23 2017 *)

CROSSREFS

Cf. A138479, A138686.

Sequence in context: A041336 A145417 A157206 * A047724 A046044 A026919

Adjacent sequences:  A138682 A138683 A138684 * A138686 A138687 A138688

KEYWORD

nonn

AUTHOR

Artur Jasinski, Mar 26 2008

STATUS

approved

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Last modified May 11 03:49 EDT 2021. Contains 343784 sequences. (Running on oeis4.)