This site is supported by donations to The OEIS Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A163457 a(n) = the smallest divisor of n such that this and all greater divisors of n are non-coprime to each other. 1
 2, 3, 2, 5, 3, 7, 2, 3, 5, 11, 4, 13, 7, 5, 2, 17, 3, 19, 5, 7, 11, 23, 4, 5, 13, 3, 7, 29, 6, 31, 2, 11, 17, 7, 6, 37, 19, 13, 8, 41, 7, 43, 11, 9, 23, 47, 4, 7, 5, 17, 13, 53, 3, 11, 8, 19, 29, 59, 6, 61, 31, 9, 2, 13, 11, 67, 17, 23, 10, 71, 9, 73, 37, 5, 19, 11, 13, 79, 8, 3, 41, 83, 12, 17 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 LINKS Alois P. Heinz, Table of n, a(n) for n = 2..5000 EXAMPLE The divisors of 30 are 1,2,3,5,6,10,15,30. 5 is coprime to 6, so a(30) >= 6. Checking the greatest common divisors of all pairs of distinct divisors >= 6: GCD(6,30)=6, GCD(6,15)=3, GCD(6,10)=2, GCD(10,30)=10, GCD(10,15)=5, and GCD(15,30) = 15. Since all of these GCD's are >= 2, then a(30) = 6. MAPLE with(numtheory): a:= proc(n) local l, j, m, s, h, k; l:= sort([divisors(n) []]); m:= nops(l); h:= m; s:= 1; k:= m; do for j from k to s by -1 do if igcd (l[k], l[j])>1 then h:=j else break fi od; s:= h; k:= k-1; if k

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 January 17 18:27 EST 2019. Contains 319250 sequences. (Running on oeis4.)