A288469 a(n) = n if n is a nonprime, otherwise take the prime index of n and repeat until you get a nonprime which is then a(n).

1, 1, 1, 4, 1, 6, 4, 8, 9, 10, 1, 12, 6, 14, 15, 16, 4, 18, 8, 20, 21, 22, 9, 24, 25, 26, 27, 28, 10, 30, 1, 32, 33, 34, 35, 36, 12, 38, 39, 40, 6, 42, 14, 44, 45, 46, 15, 48, 49, 50, 51, 52, 16, 54, 55, 56, 57, 58, 4, 60, 18, 62, 63, 64, 65, 66, 8, 68, 69, 70, 20, 72, 21, 74, 75, 76, 77, 78, 22, 80, 81, 82, 9, 84, 85, 86

Offset: 1

Author

Peter Weiss, Jun 09 2017

Keywords

• nonn

Comments

a(n) = 1 for n in A007097. - Robert Israel, Jun 09 2017

Examples

			For n = 17:  17 is a prime, so you take the prime index of 17 which is 7. 7 is a prime, so you take the prime index of 7 which is 4. 4 is a nonprime, so a(17) = 4.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000720, A007097, A010051, A114537.

Programs

Maple

f:= proc(n) option remember; if isprime(n) then procname(numtheory:-pi(n)) else n fi end proc:
map(f, [$1..100]); # Robert Israel, Jun 09 2017

Mathematica

Table[If[!PrimeQ@ n, n, NestWhile[PrimePi, n, PrimeQ]], {n, 86}] (* Michael De Vlieger, Jun 09 2017 *)

PARI

a(n)=while(isprime(n), n=primepi(n)); n \\ Charles R Greathouse IV, Jun 09 2017

Formula

From Robert Israel, Jun 09 2017: (Start)

a(n) = n + A010051(n)*(a(A000720(n))-n).

a(A114537(n,k)) = A114537(n,1). (End)