A087875 a[n] = pi[n-pi[n-1]] + a[n - a[n-2]], where pi(x) = number of primes <= x.

1, 1, 2, 3, 4, 4, 4, 5, 7, 7, 7, 8, 8, 8, 8, 9, 12, 12, 9, 10, 14, 14, 13, 13, 14, 15, 15, 16, 16, 16, 16, 17, 20, 21, 17, 17, 19, 23, 19, 21, 24, 24, 19, 20, 26, 26, 25, 25, 24, 25, 26, 27, 27, 27, 28, 28, 29, 29, 30, 30, 30, 31, 34, 34, 31, 32, 32, 32, 34, 38, 34, 36, 35, 39, 37

Offset

1,3

Comments

A reinversion-type sequence using pi as the inverse and the Hofstadter Q-numbers A005185 as the pattern sequence.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Mathematica

hrid[n] =PrimePi[n-PrimePi[n-1]] + hrid[n - hrid[n-2]] digits=256 a=Table[hrid[n], {n, 1, digits}]

Prog

(Haskell)
import Data.List (genericIndex)
a087875 n = genericIndex a087875_list (n-1)
a087875_list = 1 : 1 : zipWith (+)
   (map a087875 $ zipWith (-) [3..] a087875_list)
   (map a000720 $ zipWith (-) [3..] $ tail a000720_list)
-- Reinhard Zumkeller, Sep 21 2014

Crossrefs

Cf. A005185.

Cf. A000720.

Sequence in context: A120508 A199332 A029085 * A195848 A342731 A099777

Adjacent sequences: A087872 A087873 A087874 * A087876 A087877 A087878

Keyword

nonn

Author

Roger L. Bagula, Oct 11 2003

Status

approved