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Search: id:A137691
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| A137691 |
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Indices n such that A128646(n)+1 is prime, where A128646 = denominators of partial sums of 1/(p(i)-1). |
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+0
2
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| 1, 2, 3, 4, 5, 6, 10, 11, 12, 13, 14, 18, 38, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 475, 476, 477, 478, 479, 488, 489, 490, 491, 492, 493, 858, 859, 860, 861, 862, 863, 864, 2670, 3261, 3262, 3263, 3264, 3265, 4819, 6034, 6035, 6036, 6037, 6038
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Terms corresponding to indices n = a(k) > 1000 are not certified primes but at least probable primes. Is there a simple explanation for the large gaps between a(k)=38 and a(k+1)=376; a(k)=864 and a(k+1)=2670, etc. ?
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EXAMPLE
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n=3 is in this sequence because A128646(n)+1 = 5 is a prime (where A128646(3) is the denominator of 1/(2-1) + 1/(3-1) + 1/(5-1) = 7/4).
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PROGRAM
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(PARI) print_A137691(i=0/*start checking at i+1*/)={local(s=sum(j=1, i, 1/(prime(j)-1))); while(1, while(!ispseudoprime(1+denominator(s+=1/(prime(i++)-1))), ); print1(i", "))
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CROSSREFS
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Cf. A128646, A137689-A137692, A092063.
Sequence in context: A007093 A047423 A032970 this_sequence A158520 A032868 A032341
Adjacent sequences: A137688 A137689 A137690 this_sequence A137692 A137693 A137694
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KEYWORD
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hard,nonn
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AUTHOR
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M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Feb 07 2008
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EXTENSIONS
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Edited by T. D. Noe (noe(AT)sspectra.com), Oct 30 2008
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