The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A321132 a(n) is the number of iterations of the mapping of x -> pi(x) until n reaches the main line as defined by A007097. 0
 0, 0, 0, 2, 0, 2, 3, 3, 3, 3, 0, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 0, 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS All primes are either on the main line or will join it before reaching 0, as in A060197 or 1, as in A071578. First occurrence of k, k=0,1,2,...: 1, 4, 7, 17, 59, 277, 1787, 15299, 167449, 2269733, etc. A measure of Primeness - see the Fernandez link. LINKS Neil Fernandez, An order of primeness, F(p) FORMULA a(n) = 0 iff n is a member of A007097. EXAMPLE a(10) is 3 because the tenth prime is 29 -> 10 -> 4 -> 2 and 2 is A007097(1). MATHEMATICA f[n_] := Length@ NestWhileList[PrimePi, n, ! MemberQ[{1, 2, 3, 5, 11, 31, 127, 709, 5381, 52711, 648391, 9737333, 174440041}, #] &] - 1; Array[f, 105] CROSSREFS Cf. A000720, A007097, A049076, A060197, A071578, A114537. Sequence in context: A323212 A185815 A332448 * A003987 A307302 A307297 Adjacent sequences:  A321129 A321130 A321131 * A321133 A321134 A321135 KEYWORD nonn AUTHOR Robert G. Wilson v, Oct 27 2018 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 25 23:39 EDT 2021. Contains 346294 sequences. (Running on oeis4.)