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A091985
Number of steps required for the initial value p = 10^n to reach 0 in the recurrence p = pi(p).
0
1, 4, 6, 8, 9, 10, 11, 12, 12, 13, 14, 15, 15, 16, 17, 17, 18, 19, 19, 20
OFFSET
0,2
FORMULA
pi(n) = A000720(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.
EXAMPLE
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.
PROG
(PARI) pr10n(n) = my(c); for(x=0, n, y=10^x; c=0; p=y; while(p, p = primepi(p); c++); print1(c", "))
CROSSREFS
Cf. A000720.
Sequence in context: A019516 A031977 A225668 * A091984 A365471 A228651
KEYWORD
hard,nonn
AUTHOR
Cino Hilliard, Mar 16 2004
EXTENSIONS
a(14)-a(19) from Chai Wah Wu, May 25 2018
STATUS
approved