A231470 Largest integer less than 10, coprime to n.

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

Offset

1,1

Comments

Periodic with period 210.

Motivated by A231155(n)=a(n)*(10^(n-1)-1)/9.

a(n) is in {1, 5, 7, 8, 9}. Average value is 253/30 = 8.433.... - Charles R Greathouse IV, Oct 13 2022

Links

Table of n, a(n) for n=1..98.

Index entries for linear recurrences with constant coefficients, order 210.

Example

a(210)=1 because 210=2*3*5*7 is not coprime to any number n>1, n<10.

Prog

(PARI) a(n)=for(k=1, 9, gcd(n, 10-k)==1&&return(10-k)))
(PARI) a(n)=n=n%210; (2456570291879305656378327950088507572292988734220585220471023291179171177166614 45448973642646595615830994341498146323777941833948520102560885856758200689935551 394284409822886865709103348710416026442401 \ 9^n)%9+1 \\ Charles R Greathouse IV, Oct 13 2022

Crossrefs

Cf. A231475 (analog for 5), A231471 (analog for 11), A231155.

Sequence in context: A175570 A050812 A139345 * A109942 A339745 A346929

Adjacent sequences: A231467 A231468 A231469 * A231471 A231472 A231473

Keyword

nonn,easy

Author

M. F. Hasler, Nov 09 2013

Status

approved