

A005537


Numbers n such that 4*3^n + 1 is prime.
(Formerly M0803)


4



0, 1, 2, 3, 6, 14, 15, 39, 201, 249, 885, 1005, 1254, 1635, 3306, 3522, 9602, 19785, 72698
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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 (N1/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. 3442.
H. C. Williams and C. R. Zarnke, Some prime numbers of the forms 2*3^n+1 and 2*3^n1, Math. Comp., 26 (1972), 995998.


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



