login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A197862 Prime divisor of n which appears the fewest times previously in the sequence, with ties to the larger prime. 1
2, 3, 2, 5, 3, 7, 2, 3, 5, 11, 3, 13, 7, 5, 2, 17, 3, 19, 5, 7, 11, 23, 2, 5, 13, 3, 7, 29, 5, 31, 2, 11, 17, 7, 3, 37, 19, 13, 5, 41, 7, 43, 11, 5, 23, 47, 2, 7, 2, 17, 13, 53, 3, 11, 7, 19, 29, 59, 5, 61, 31, 7, 2, 13, 11, 67, 17, 23, 7, 71, 3, 73, 37, 5, 19 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

Up to n = 100, this differs from the greatest prime factor function A006530 only at n = 24, 48, 50, 80, and 98.

LINKS

Table of n, a(n) for n=2..76.

EXAMPLE

The only prime divisor of 4 is 2, so a(4) = 2.

The prime divisors of 6 are 2 and 3; in the sequence to that point (2,3,2,5), there are two 2's and 1 3, we take the less common one, so a(6) = 3.

The prime divisors of 12 are 2 and 3; these occur equally often in the sequence to that point, so we take the larger one; a(12)=3.

PROG

(PARI) al(n)={local(ns=vector(primepi(n)), r=vector(n-1), ps);

  for(k=1, n-1,

    ps=factor(k+1)[, 1]~;

    r[k]=ps[1];

    for(j=2, #ps, if(ns[primepi(ps[j])]<=ns[primepi(r[k])], r[k]=ps[j]));

    ns[primepi(r[k])]++);

  r}

CROSSREFS

Cf. A197861, A006530.

Sequence in context: A273283 A276440 A162325 * A006530 A102095 A109395

Adjacent sequences:  A197859 A197860 A197861 * A197863 A197864 A197865

KEYWORD

nonn

AUTHOR

Franklin T. Adams-Watters, Oct 18 2011

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 11 05:41 EST 2017. Contains 295868 sequences.