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Search: id:A091985
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| A091985 |
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Number of steps required for the initial value p = 10^n to reach 0 in the recurrence p = pi(p). |
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+0
1
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| 1, 4, 6, 8, 9, 10, 11, 12, 12, 13, 14, 15, 15, 16
(list; graph; listen)
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OFFSET
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0,2
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LINKS
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Andrew Booker, The Nth Prime Page.
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FORMULA
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pi(n) = number of primes less than or equal to n. By repeating n=pi(n), n will reach 0 in a finite number of steps.
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EXAMPLE
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Pi(100) = 25
Pi(25) = 9
Pi(9) = 4
Pi(4) = 2
Pi(2) = 1
Pi(1) = 0
Total steps to reach 0 = 6. Thus 6 is the 3rd entry in the sequence corresponding to n=2.
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PROGRAM
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(PARI) pr10n(n) = { local c; for(x=0, n, y=10^x; c=0; p=y; while(p, p = pi(p); c++); print1(c", ") ) } pi(n) = { local ct; ct=0; forprime(x=1, n, ct++); return(ct) \pi(x) prime count function
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CROSSREFS
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Sequence in context: A085049 A019516 A031977 this_sequence A091984 A045762 A047748
Adjacent sequences: A091982 A091983 A091984 this_sequence A091986 A091987 A091988
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KEYWORD
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hard,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Mar 16 2004
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