A108908 Largest n-digit number coprime to n.

9, 99, 998, 9999, 99999, 999997, 9999999, 99999999, 999999998, 9999999999, 99999999999, 999999999997, 9999999999999, 99999999999999, 999999999999998, 9999999999999999, 99999999999999999, 999999999999999997

Offset

1,1

Comments

a(286) = 10^286 - 5 is the first term with a(n) < 10^n - 3. - Rick L. Shepherd, Jul 21 2005

Links

Robert Israel, Table of n, a(n) for n = 1..996

Maple

f:= proc(n) local k;
    for k from 10^n-1 by -1 do if igcd(k, n) = 1 then return k fi od
end proc:
map(f, [$1..20]); # Robert Israel, Mar 17 2026

Mathematica

f[n_] := Block[{k=10^n-1}, While[ GCD[n, k]>1, k-- ]; k]; Table[ f[n], {n, 18}] (* Robert G. Wilson v, Jul 21 2005 *)

Prog

(PARI) a(n) = my(m=10^n-1); while(gcd(m, n)>1, m--); m \\ Rick L. Shepherd, Jul 21 2005

Crossrefs

Cf. A394352, A394357.

Sequence in context: A070843 A261512 A242809 * A116260 A103456 A002283

Adjacent sequences: A108905 A108906 A108907 * A108909 A108910 A108911

Keyword

base,easy,nonn

Author

Amarnath Murthy, Jul 19 2005

Extensions

More terms from Rick L. Shepherd and Robert G. Wilson v, Jul 21 2005

Status

approved