A231471 - OEIS

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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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

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

LINKS

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

EXAMPLE

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.

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 *)

PROG

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

CROSSREFS

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

Sequence in context: A070562 A216557 A070641 * A063661 A154533 A167608

Adjacent sequences: A231468 A231469 A231470 * A231472 A231473 A231474

KEYWORD

nonn,easy

AUTHOR

M. F. Hasler, Nov 09 2013

STATUS

approved