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

1,1

Links

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

Wikipedia, GCD

Formula

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

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

Example

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.

Mathematica

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

Prog

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

Crossrefs

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

Sequence in context: A367126 A136627 A108171 * A106055 A171783 A251767

Adjacent sequences: A231472 A231473 A231474 * A231476 A231477 A231478

Keyword

nonn,easy

Author

M. F. Hasler, Nov 09 2013

Status

approved