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A005537 Numbers n such that 4*3^n + 1 is prime.
(Formerly M0803)
5
0, 1, 2, 3, 6, 14, 15, 39, 201, 249, 885, 1005, 1254, 1635, 3306, 3522, 9602, 19785, 72698 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(20) > 2*10^5. - Robert Price, Nov 23 2013

Primes resulting from a(1)-a(19) are confirmed primes (not probable primes) using BLS (N-1/N+1) test in pfgw. - Robert Price, Nov 23 2013

REFERENCES

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

LINKS

Table of n, a(n) for n=1..19.

C. K. Caldwell, The Prime Pages

Douglas E. Iannucci, Deng Moujie and Graeme L. Cohen, On Perfect Totient Numbers, J. Integer Sequences, 6 (2003), #03.4.5.

P. Loomis, M. Plytage and J. Polhill, Summing up the Euler 'phi' function, The College Mathematics Journal, vol. 39 (2008), pp. 34-42.

H. C. Williams and C. R. Zarnke, Some prime numbers of the forms 2*3^n+1 and 2*3^n-1, Math. Comp., 26 (1972), 995-998.

PROG

(PARI) a(n) = isprime(4*3^n + 1) \\ Michel Marcus, Jul 12 2013

CROSSREFS

Sequence in context: A121556 A123041 A078557 * A193093 A182756 A152092

Adjacent sequences:  A005534 A005535 A005536 * A005538 A005539 A005540

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Chris K. Caldwell

EXTENSIONS

a(15)-a(17) from Douglas Burke (dburke(AT)nevada.edu)

a(18) from Mohammed Bouayoun (Mohammed.Bouayoun(AT)sanef.com), Jan 26 2004

a(19) from Robert Price, Nov 23 2013

STATUS

approved

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Last modified November 21 21:29 EST 2014. Contains 249791 sequences.