The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A089992 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
Showing entries 1-10 | older changes

A089992

Second prime divisor of numbers that are not powers of primes (A024619).
(history; published version)

#12 by Alois P. Heinz at Wed Apr 14 10:04:27 EDT 2021

STATUS

proposed

approved

#11 by Michel Marcus at Wed Apr 14 10:00:04 EDT 2021

STATUS

editing

proposed

#10 by Michel Marcus at Wed Apr 14 09:59:57 EDT 2021

PROG

(PARI) f(n) = a=factor(n); v=a[, 1]; ln=length(v); if(ln>1, return(v[2])) g(m) = for(x=2, m, if(f(x)>0, print1(f(x)", ")));

g(m) = for(x=2, m, if(f(x)>0, print1(f(x)", ")));

STATUS

approved

editing

#9 by Michel Marcus at Mon Apr 12 04:35:53 EDT 2021

STATUS

reviewed

approved

#8 by Joerg Arndt at Mon Apr 12 03:32:36 EDT 2021

STATUS

proposed

reviewed

#7 by Amiram Eldar at Mon Apr 12 02:19:44 EDT 2021

STATUS

editing

proposed

#6 by Amiram Eldar at Mon Apr 12 02:15:13 EDT 2021

NAME

Second prime divisor of n if it existsnumbers that are not powers of primes (A024619).

FORMULA

a(n) = A119288(A024619(n)). - Amiram Eldar, Apr 12 2021

CROSSREFS

Cf. A024619, A119288, A089993.

#5 by Amiram Eldar at Mon Apr 12 02:13:29 EDT 2021

LINKS

Amiram Eldar, <a href="/A089992/b089992.txt">Table of n, a(n) for n = 1..10000</a>

#4 by Amiram Eldar at Mon Apr 12 02:13:08 EDT 2021

OFFSET

2,1,1

MATHEMATICA

Select[Table[If[Length[(f = FactorInteger[n])] > 1, f[[2, 1]], 1], {n, 1, 150}], # > 1 &]

EXTENSIONS

Offset corrected by Amiram Eldar, Apr 12 2021

STATUS

approved

editing

#3 by N. J. A. Sloane at Tue Oct 01 17:57:56 EDT 2013

AUTHOR

_Cino Hilliard (hillcino368(AT)gmail.com), _, Jan 14 2004

Discussion

Tue Oct 01

17:57

OEIS Server: https://oeis.org/edit/global/1955