A214720 Least m>0 such that n^2-m and n-m are relatively prime.

2, 1, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2

Offset: 1

Author

Clark Kimberling, Jul 27 2012

Keywords

• nonn
• easy

Examples

			a(12) = 5 because of the following:
gcd(144-1,11) > 1,
gcd(144-2,10) > 1 ,
gcd(144-3,9) > 1,
gcd(144-4,8) >1,
gcd(144-5,7) = 1.
		

Links

• Clark Kimberling, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A214716, A053669.

Programs

Maple

A214720 := proc(n)
    for m from 1 do
        if igcd(n^2-m,n-m) =1  then
            return m;
        end if;
    end do:
end proc: # R. J. Mathar, Mar 30 2014

Mathematica

Table[m = 1; While[GCD[5^n - m, n - m] != 1, m++]; m, {n, 1, 140}]