A064960 The prime then composite recurrence; a(2n) = a(2n-1)-th prime and a(2n+1) = a(2n)-th composite and a(1) = 1.
1, 2, 6, 13, 22, 79, 108, 593, 722, 5471, 6290, 62653, 69558, 876329, 951338, 14679751, 15692307, 289078661, 305618710, 6588286337, 6908033000, 171482959009, 178668550322, 5040266614919, 5225256019175, 165678678591359, 171068472492228, 6039923990345039
Offset: 1
Keywords
Links
- Chai Wah Wu, Table of n, a(n) for n = 1..31
- Andrew R. Booker, The Nth Prime Page
- N. Fernandez, An order of primeness, F(p)
- N. Fernandez, An order of primeness [cached copy, included with permission of the author]
Crossrefs
Programs
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Mathematica
Composite[n_Integer] := FixedPoint[n + PrimePi[ # ] + 1 &, n + PrimePi[n] + 1]; a = {1}; b = 1; Do[ If[ !PrimeQ[b], b = Prime[b], b = Composite[b]]; a = Append[a, b], {n, 1, 23}]; a -
Python
from functools import cache from sympy import prime, composite @cache def A064960(n): return 1 if n == 1 else composite(A064960(n-1)) if n % 2 else prime(A064960(n-1)) # Chai Wah Wu, Jan 01 2022
Extensions
a(26)-a(28) from Chai Wah Wu, May 07 2018