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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, 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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

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

LINKS

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

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)

EXAMPLE

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.

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 *)

PROG

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

CROSSREFS

Cf. A000720, A007097, A010051, A114537.

Sequence in context: A318876 A330356 A329428 * A076717 A200360 A228451

Adjacent sequences:  A288466 A288467 A288468 * A288470 A288471 A288472

KEYWORD

nonn

AUTHOR

Peter Weiss, Jun 09 2017

STATUS

approved

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Last modified September 30 13:46 EDT 2020. Contains 337439 sequences. (Running on oeis4.)