The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A090544

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A090544

Let f(k) = k + pi(k); a(n) = least number of steps for f(f(f(...(n)))) to reach a prime.
(history; published version)

#8 by Michel Marcus at Mon Jul 31 05:26:22 EDT 2023

STATUS

reviewed

approved

#7 by Joerg Arndt at Mon Jul 31 05:24:26 EDT 2023

STATUS

proposed

reviewed

#6 by Jean-François Alcover at Mon Jul 31 04:41:43 EDT 2023

STATUS

editing

proposed

#5 by Jean-François Alcover at Mon Jul 31 04:41:27 EDT 2023

MATHEMATICA

f[k_] := k + PrimePi[k];

a[n_] := NestWhileList[f, f[n], CompositeQ] // Length;

Table[a[n], {n, 2, 102}] (* Jean-François Alcover, Jul 31 2023 *)

STATUS

approved

editing

#4 by N. J. A. Sloane at Thu Dec 05 19:56:38 EST 2013

AUTHOR

_Amarnath Murthy (amarnath_murthy(AT)yahoo.com), _, Dec 09 2003

Discussion

Thu Dec 05

19:56

OEIS Server: https://oeis.org/edit/global/2075

#3 by Russ Cox at Sat Mar 31 13:21:28 EDT 2012

EXTENSIONS

More terms from Frank _Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), _, Apr 26 2006

Discussion

Sat Mar 31

13:21

OEIS Server: https://oeis.org/edit/global/884

#2 by N. J. A. Sloane at Fri May 19 03:00:00 EDT 2006

DATA

1, 1, 3, 3, 2, 1, 2, 1, 4, 6, 1, 1, 3, 2, 5, 8, 4, 3, 2, 1, 4, 2, 7, 3, 10, 2, 1, 5, 3, 3, 1, 6, 2, 9, 1, 5, 3, 4, 2, 3, 2, 2, 5, 1, 8, 9, 3, 4, 2, 3, 1, 12, 2, 1, 10, 1, 4, 2, 7, 1, 8, 2, 3, 1, 2, 2, 3, 11, 1, 4, 9, 24, 3, 5, 1, 6, 18, 1, 7, 1, 2, 10, 1, 6, 1, 2, 10, 1, 8, 3, 8, 3, 23, 2, 4, 12, 5, 17, 3, 1, 6

KEYWORD

more,nonn,new

nonn

EXTENSIONS

More terms from Frank Adams-Watters (FrankTAW(AT)Netscape.net), Apr 26 2006

#1 by N. J. A. Sloane at Thu Feb 19 03:00:00 EST 2004

NAME

Let f(k) = k + pi(k); a(n) = least number of steps for f(f(f(...(n)))) to reach a prime.

DATA

1, 1, 3, 3, 2, 1, 2, 1, 4

OFFSET

2,3

EXAMPLE

a(4) = 3, f(4) = 4+2 = 6, f(6) = 6+3 = 9, f(9)= 9+4 = 13 is prime.

a(10) = 4, f(10) = 10+4=14, f(14) = 14+6 = 20, f(20) = 20+8 = 28, f(28) = 28+9 = 37.

CROSSREFS

Cf. A090545, A090546.

KEYWORD

more,nonn

AUTHOR

Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Dec 09 2003

STATUS

approved