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A002504 Numbers x such that 1 + 3x*(x-1) is a ("cuban") prime (cf. A002407).
(Formerly M0522 N0188)
6
2, 3, 4, 5, 7, 10, 11, 12, 14, 15, 18, 24, 25, 26, 28, 29, 31, 33, 35, 38, 39, 42, 43, 46, 49, 50, 53, 56, 59, 63, 64, 67, 68, 75, 81, 82, 87, 89, 91, 92, 94, 96, 106, 109, 120, 124, 126, 129, 130, 137, 141, 143, 148, 154, 157, 158, 159, 165, 166, 171, 172 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

A. J. C. Cunningham, On quasi-Mersennian numbers, Mess. Math., 41 (1912), 119-146.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

EXAMPLE

a(1) = 2 since A002407(1) = 7 = 1 + 3k*(k-1) with k=2 is the smallest prime of that form.

MATHEMATICA

Select[Range[500], PrimeQ[1 + 3 # (# - 1)] &] (* T. D. Noe, Jan 30 2013 *)

PROG

(PARI) for(k=1, 999, isprime(3*k*(k-1)+1)&print1(k", ")) \\ M. F. Hasler, Nov 28 2007

CROSSREFS

Cf. A002407, A133431.

Sequence in context: A047502 A117092 A285276 * A133431 A305705 A123091

Adjacent sequences:  A002501 A002502 A002503 * A002505 A002506 A002507

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

EXTENSIONS

Edited, updated (1 is no longer regarded as a prime) and extended by M. F. Hasler, Nov 28 2007

STATUS

approved

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Last modified October 6 21:32 EDT 2022. Contains 357270 sequences. (Running on oeis4.)