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A079363
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Primes of the form 2*3^n-1.
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9
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5, 17, 53, 4373, 13121, 1062881, 6973568801, 188286357653, 15251194969973, 100063090197999413, 1046695266054721074427023041, 763040848953891663257299797617, 556256778887387022514571552463521
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Sum of reciprocals = 0.2779972845973183835923785945..
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 1..20
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MATHEMATICA
| Select[2*3^Range[100]-1, PrimeQ]
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PROG
| (PARI) \ Primes in the sequence of sums of alternating powers of 3 pseq3(n) = { j=a=1; p=1; sr=0; while(j<=n, a = a + 3^(p); if(isprime(a), print1(a" "); sr+=1.0/a; ); a = a+3^(p-1); if(isprime(a), print1(a" "); sr+=1.0/a; ); p+=1; j+=2; ); print(); print(sr); }
(MAGMA) [a: n in [1..200] | IsPrime(a) where a is 2*3^n-1 ]; // Vincenzo Librandi, Dec 09 2011
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CROSSREFS
| Cf. A003306 (n such that 2*3^n+1 is prime), A003307 (n such that 2*3^n-1 is prime).
Sequence in context: A146006 A161470 A195689 * A034346 A055419 A027091
Adjacent sequences: A079360 A079361 A079362 * A079364 A079365 A079366
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KEYWORD
| nonn
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AUTHOR
| Cino Hilliard (hillcino368(AT)gmail.com), Feb 15 2003
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