A231475 Largest integer less than 5 and coprime to n.

4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4, 3, 4, 1, 4, 3, 4

Offset: 1

Author

M. F. Hasler, Nov 09 2013

Keywords

• nonn
• easy

Examples

			a(1)=4 because this is the largest integer less than 5 and it's coprime to n=1.
a(2)=3 because 4 is not coprime to 2 but 3 is.
a(6)=1 because no other positive integer n<4 is coprime to 6=2*3.
		

Links

• Antti Karttunen, Table of n, a(n) for n = 1..65537
• Wikipedia, GCD

Crossrefs

Cf. A231471 (analog for 11), A231470 (analog for 10), A231155.

Programs

Mathematica

Max[Table[If[CoprimeQ[#,d],d,0],{d,4}]]&/@Range[100] (* Harvey P. Dale, Aug 27 2022 *)

PARI

A231475(n, m=5) = for(k=1, m, gcd(n, m-k)==1&&return(m-k));

Formula

a(2k+1) = 4 = 2*2.

a(2k) = 1 if 3|k, otherwise a(2k)=3. - Jon Perry, Nov 09 2013