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A005538 Numbers n such that 8*3^n + 1 is prime.
(Formerly M1729)
1
2, 7, 8, 10, 22, 52, 58, 76, 130, 143, 331, 332, 980, 1282, 1655, 4031, 4600, 18880, 89482, 130592 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Contribution from R. J. Mathar, Mar 01 2010: (Start)

The row r=4 in the table of "Numbers n such that 2*r*3^n+1 is prime":

.1,..2,..4,..5,..6,..9,.16,.17,.30,.54,.57,.60,.65,.132,.180,

.1,..2,..3,..6,.14,.15,.39,201,249,

.1,..3,..4,..5,..8,.15,.16,.29,.53,.56,.59,.64,131,179,

.2,..7,..8,.10,.22,.52,.58,.76,130,143,

.1,..3,..4,..7,..9,.12,.18,.22,102,112,157,162,289,

.1,..2,..5,.13,.14,.38,200,248,

.1,..2,..3,.18,.22,.26,.27,.33,.39,.57,.62,.94,145,246,

.3,..4,..5,.12,.24,.36,.77,195,296,297,

.2,..3,..4,..7,.14,.15,.28,.52,.55,.58,.63,130,178,

.1,..2,..3,..4,..5,..8,.16,.19,.28,.50,134,280,

.1,..2,..4,..5,.10,.12,.14,.24,.34,.37,.52,.56,.65,.68,.96,106,128,156,169,236,254,

.1,..6,..7,..9,.21,.51,.57,.75,129,142,

.1,.12,.15,.17,.20,.29,.31,.32,.35,.37,.77,.95,193,203,224,296,

.3,..4,..8,.11,.14,.15,.18, (End)

a(21) > 2*10^5. - Robert Price, Mar 16 2014

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..20.

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.

MATHEMATICA

Select[Range[5000], PrimeQ[8*3^# + 1] &] (* Michael De Vlieger, Jun 26 2017 *)

PROG

(PARI) v=[ ]; for(n=0, 2000, if(isprime(8*3^n+1), v=concat(v, n), )); v

CROSSREFS

Sequence in context: A075766 A258823 A226612 * A206331 A053013 A070044

Adjacent sequences:  A005535 A005536 A005537 * A005539 A005540 A005541

KEYWORD

nonn,hard

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from Douglas Burke (dburke(AT)nevada.edu)

a(19)-a(20) from Robert Price, Mar 16 2014

STATUS

approved

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Last modified April 21 04:56 EDT 2019. Contains 322310 sequences. (Running on oeis4.)