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Search: id:A079363
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| A079363 |
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Primes of the form 2*3^n-1. |
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+0
9
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| 5, 17, 53, 4373, 13121, 1062881, 6973568801, 188286357653, 15251194969973, 100063090197999413, 1046695266054721074427023041, 763040848953891663257299797617, 556256778887387022514571552463521
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Sum of reciprocals = 0.2779972845973183835923785945..
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MATHEMATICA
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Select[2*3^Range[100]-1, PrimeQ]
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PROGRAM
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(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); }
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CROSSREFS
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Cf. A003306 (n such that 2*3^n+1 is prime), A003307 (n such that 2*3^n-1 is prime).
Sequence in context: A146063 A146006 A161470 this_sequence A034346 A055419 A027091
Adjacent sequences: A079360 A079361 A079362 this_sequence A079364 A079365 A079366
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Feb 15 2003
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