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Search: id:A137689
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| A137689 |
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Indices n such that A128646(n)-1 is prime, where A128646 = denominator of partial sums of 1/(p(i)-1). |
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4
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| 3, 4, 5, 7, 8, 9, 10, 11, 15, 16, 23, 24, 26, 47, 48, 54, 78, 79, 80, 243, 244, 245, 246, 247, 367, 368, 369, 370, 371, 372, 373, 374, 375, 447, 453, 635, 636, 1656, 1657, 1658, 1659, 1660
(list; graph; listen)
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OFFSET
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1,1
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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)=80, a(k+1)=243 and a(k)=636, a(k+1)=1656 ?
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PROGRAM
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(PARI) print_A137689(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, A137690-A137692, A092063.
Sequence in context: A078358 A039131 A072225 this_sequence A081690 A081688 A118170
Adjacent sequences: A137686 A137687 A137688 this_sequence A137690 A137691 A137692
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KEYWORD
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hard,more,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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