A124741 a(n) = largest of those positive integers which are coprime to both n and n+1 and which are <= n.

1, 1, 1, 3, 1, 5, 5, 7, 7, 9, 7, 11, 11, 13, 13, 15, 13, 17, 17, 19, 19, 21, 19, 23, 23, 25, 25, 27, 23, 29, 29, 31, 31, 33, 31, 35, 35, 37, 37, 39, 37, 41, 41, 43, 43, 45, 43, 47, 47, 49, 49, 51, 49, 53, 53, 55, 55, 57, 53, 59, 59, 61, 61, 63, 61, 65, 65, 67, 67, 69, 67, 71, 71

Offset: 1

Author

Leroy Quet, Nov 06 2006

Keywords

• nonn

Examples

			The positive integers which are coprime to 8 and which are <= 8 are 1,3,5,7. The positive integers which are coprime to 9 and which are <= 9 are 1, 2,4,5,7,8. So a(8) = 7, which is the largest of those integers in both these sequences (1,5,7).
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A057475, A124738, A124739, A124740.

Programs

Mathematica

f[n_] := Last @ Select[Range[n], GCD[n, # ] == GCD[n + 1, # ] == 1 &];Table[f[n], {n, 75}] (* Ray Chandler, Nov 10 2006 *)
Join[{1},Table[Max[Intersection[Select[Range[n-1],CoprimeQ[ #,n]&],Select[ Range[n-1],CoprimeQ[#,n+1]&]]],{n,2,80}]] (* Harvey P. Dale, Jul 08 2018 *)

Extensions

Extended by Ray Chandler, Nov 10 2006