The On-Line Encyclopedia of Integer Sequences (OEIS)

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A247977

If n = 1 or prime, then a(n) = 0; otherwise, if n is a preprime of k-th kind, then a(n) = k.
(history; published version)

#18 by N. J. A. Sloane at Mon Jan 02 12:30:50 EST 2023

LINKS

Vladimir Shevelev , <a href="http://list.seqfan.eu/pipermailoldermail/seqfan/2014-September/013643.html">A classification of the positive integers over primes</a>

Discussion

Mon Jan 02

12:30

OEIS Server: https://oeis.org/edit/global/2957

#17 by Bruno Berselli at Wed Mar 08 09:10:03 EST 2017

STATUS

reviewed

approved

#16 by Joerg Arndt at Wed Mar 08 09:01:15 EST 2017

STATUS

proposed

reviewed

#15 by Indranil Ghosh at Wed Mar 08 08:02:31 EST 2017

STATUS

editing

proposed

#14 by Indranil Ghosh at Wed Mar 08 08:01:31 EST 2017

LINKS

Indranil Ghosh, <a href="/A247977/b247977.txt">Table of n, a(n) for n = 1..10000</a>

MATHEMATICA

lpf[n_]:= FactorInteger[n][[1, 1]]; Table[If[n==1 || PrimeQ[n], 0, PrimePi[Sqrt[n]] - PrimePi[lpfFactorInteger[n][[1, 1]]] + 1], {n, 1, 125}] (* Indranil Ghosh, Mar 08 2017 *)

PROG

(PARI) lpffor(n=1, 125, print1(if(n==1 || isprime(n), 0, primepi(sqrt(n) = ) - primepi(vecmin(factor(n)[, 1]); ) + 1), ", ")) \\ _Indranil Ghosh_, Mar 08 2017

for(n=1, 125, print1(if(n==1 || isprime(n), 0, primepi(sqrt(n)) - primepi(lpf(n)) + 1), ", ")) \\ Indranil Ghosh, Mar 08 2017

#13 by Indranil Ghosh at Wed Mar 08 07:54:19 EST 2017

PROG

(PARI) lpf(n) = vecmin(factor(n)[, 1]);

for(n=1, 125, print1(if(n==1 || isprime(n), 0, primepi(sqrt(n)) - primepi(lpf(n)) + 1), ", ")) \\ Indranil Ghosh, Mar 08 2017

#12 by Indranil Ghosh at Wed Mar 08 05:23:54 EST 2017

MATHEMATICA

lpf[n_]:= FactorInteger[n][[1, 1]]; Table[If[n==1 || PrimeQ[n], 0, PrimePi[Sqrt[n]] - PrimePi[lpf[n]] + 1], {n, 1, 125}] (* Indranil Ghosh, Mar 08 2017 *)

STATUS

approved

editing

#11 by N. J. A. Sloane at Sun Apr 17 09:20:26 EDT 2016

STATUS

editing

approved

#10 by N. J. A. Sloane at Sun Apr 17 09:20:23 EDT 2016

COMMENTS

Preprimes of k-th kind are defined in comment of in A247395.

STATUS

approved

editing

#9 by Michael Somos at Wed Oct 22 11:15:46 EDT 2014

STATUS

proposed

approved