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Search: id:A080696
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| A080696 |
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Piptorial primes = product of pips or prime-index-primes. |
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+0
3
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| 3, 15, 165, 2805, 86955, 3565155, 210344145, 14093057715, 1169723790345, 127499893147605, 16192486429745835, 2542220369470096095, 455057446135147201005, 86915972211813115391955
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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The numbers after the first always end in 5. This is obvious since all pips are odd and their product (excluding 5) = 2k+1 and 5*(2k+1) = 10k+5. Sum of reciprocals converges to 0.4064288978193657814428353009..
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FORMULA
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prime(prime(1)), prime(prime(1))*prime(prime(2)), ...
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EXAMPLE
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pip(1) = 3,pip(2)=5,pip(3)=11 piptorial(3) = 3*5*11 = 165
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PROGRAM
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(PARI) piptorial(n) = {sr=0; pr=1; for(x=1, n, y=prime(prime(x)); pr*=y; print1(pr" "); sr+=1.0/pr; ); print(); print(sr) }
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CROSSREFS
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Sequence in context: A105611 A108975 A097489 this_sequence A015013 A132683 A059386
Adjacent sequences: A080693 A080694 A080695 this_sequence A080697 A080698 A080699
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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), Mar 04 2003
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