A231471 Largest integer less than 11 and coprime to n.

10, 9, 10, 9, 9, 7, 10, 9, 10, 9, 10, 7, 10, 9, 8, 9, 10, 7, 10, 9, 10, 9, 10, 7, 9, 9, 10, 9, 10, 7, 10, 9, 10, 9, 9, 7, 10, 9, 10, 9, 10, 5, 10, 9, 8, 9, 10, 7, 10, 9, 10, 9, 10, 7, 9, 9, 10, 9, 10, 7, 10, 9, 10, 9, 9, 7, 10, 9, 10, 9, 10, 7, 10, 9, 8, 9, 10, 7, 10, 9

Offset: 1

Author

M. F. Hasler, Nov 09 2013

Keywords

• nonn
• easy

Comments

Motivated by the m = 10 analog A231470 which in turn was motivated by A231155, simply a repetition of (n-1) times the same digit A231470(n).

Periodic with period 210. Possible values are 1, 5, 7, 8, 9, 10. - Robert Israel, Jul 03 2020

Examples

			a(1) = 10 because 10 is the largest integer less than 11 and it's coprime to 1.
a(2) = 9 because 10 is not coprime to 2 but 9 is.
a(6) = 7 because 10, 9 and 8 are not coprime to 6 = 2*3.
a(210) = 1 because 210 = 2*3*5*7 is not coprime to any number n > 1, n < 11.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A231475 (analog for 5), A231470 (analog for 10), A231155.

Programs

Maple

f:= proc(n) local k;
for k from 10 by -1 do if igcd(n,k)=1 then return k fi od
end proc:
map(f, [$1..210]); # Robert Israel, Jul 03 2020

Mathematica

Table[m = 10; While[GCD[m, n] != 1, m--]; m, {n, 75}] (* Alonso del Arte, Nov 09 2013 *)

PARI

a(n,m=11)=for(k=1,m,gcd(n,m-k)==1&&return(m-k))