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A242330 Numbers k such that k^2 + 2 is a semiprime. 4
2, 6, 7, 11, 12, 17, 18, 27, 29, 35, 37, 42, 43, 48, 51, 53, 54, 55, 60, 65, 66, 69, 72, 73, 75, 79, 83, 84, 87, 90, 93, 97, 115, 119, 125, 132, 133, 135, 137, 141, 144, 150, 153, 155, 159, 161, 165, 169, 174, 183, 186, 187, 189, 191, 192, 195, 198 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The semiprimes of this form are: 6, 38, 51, 123, 146, 291, 326, 731, 843, 1227, 1371, 1766, 1851, 2306, 2603, 2811, 2918, 3027, 3602, ...

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

MATHEMATICA

Select[Range[300], PrimeOmega[#^2 + 2] == 2 &]

PROG

(MAGMA) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..200] | IsSemiprime(s) where s is n^2+2];

CROSSREFS

Cf. A056899, A067201, A085722, A242331, A242332, A242333.

Sequence in context: A283766 A047216 A244970 * A039568 A032926 A214991

Adjacent sequences:  A242327 A242328 A242329 * A242331 A242332 A242333

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, May 14 2014

STATUS

approved

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Last modified March 29 02:15 EDT 2020. Contains 333104 sequences. (Running on oeis4.)