A190911 Least number coprime to n and n+3.

3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 3, 7, 3, 3, 7, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 3, 7, 3, 3, 7, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 3, 11, 3, 3, 7, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 3, 7, 3, 3, 11, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 3, 7, 3, 3, 7, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 3

Offset

1,1

Comments

This is to n+3 as A053670 is to n+1. This is the 3rd row of the array A(k,n) = Least number coprime to n and n+k where A053670 is the 1st row. First n for which a(n) = (3, 5, 7, 11, 13, 17, 19, ...) are A191112 = (1, 3, 12, 42, 165, 3000, 2142, ...).

Links

Nathaniel Johnston, Table of n, a(n) for n = 1..10000

Example

a(12) = 7 because the prime factors of 12 and 12+3 = 15 are {2, 3, 5} and the next available prime is 7.

Maple

A190911 := proc(n) local k: for k from 3 by 2 do if(gcd(k, n)=1 and gcd(k, n+3)=1)then return k: fi: od: end: seq(A190911(n), n=1..100); # Nathaniel Johnston, May 26 2011

Crossrefs

Cf. A053669-A053674, A191112.

Sequence in context: A372041 A206550 A284723 * A204903 A054906 A269733

Adjacent sequences: A190908 A190909 A190910 * A190912 A190913 A190914

Keyword

nonn,easy

Author

Jonathan Vos Post, May 26 2011

Extensions

a(15) corrected by Nathaniel Johnston, May 26 2011

Status

approved