A073257 Smallest k such that gcd(c(k),k) = gcd(A002808(k),k) = A064814(k) = n.

1, 2, 12, 20, 5, 6, 7, 64, 234, 50, 55, 24, 26, 28, 30, 32, 629, 1008, 209, 220, 231, 1012, 506, 168, 425, 182, 189, 2716, 2204, 1080, 93, 96, 99, 2176, 105, 4428, 1369, 5586, 1755, 1800, 6109, 2478, 2279, 3916, 5760, 644, 4606, 1920, 1960, 10250, 2040, 2444

Offset: 1

Author

Labos Elemer, Jul 22 2002

Keywords

• nonn

Examples

			50th composite is 70, gcd(50,70)=10 appears first here, a(10)=50.
		

Links

• Sean A. Irvine, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A064814, A002808, A073258.

Programs

Mathematica

f[x_] := FixedPoint[x+PrimePi[ # ]+1&, x] t=Table[0, {100}]; Do[s=GCD[f[n], n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 100000}]; t

Formula

a(n) = min{x: gcd(c(x), x)=n}, where c(x) is the x-th composite number.