A091985 Number of steps required for the initial value p = 10^n to reach 0 in the recurrence p = pi(p).

1, 4, 6, 8, 9, 10, 11, 12, 12, 13, 14, 15, 15, 16, 17, 17, 18, 19, 19, 20

Offset

0,2

Links

Table of n, a(n) for n=0..19.

Andrew Booker, The Nth Prime Page.

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

Adjacent sequences: A091982 A091983 A091984 * A091986 A091987 A091988

Keyword

hard,nonn

Author

Cino Hilliard, Mar 16 2004

Extensions

a(14)-a(19) from Chai Wah Wu, May 25 2018

Status

approved