A087271 Least number x such that gcd(x, pi(x)) = n.

1, 4, 6, 8, 50, 66, 77, 56, 27, 30, 33, 156, 169, 182, 465, 224, 238, 252, 2299, 1380, 189, 902, 207, 96, 100, 1872, 1323, 2464, 1247, 120, 1333, 3168, 528, 1258, 1295, 828, 3441, 2888, 1755, 5800, 1271, 1932, 731, 748, 765, 2852, 2209, 11568, 2695, 4000

Offset: 1

Author

Labos Elemer, Sep 16 2003

Keywords

• nonn

Examples

			n=253: a(253)=91586, pi(91586)=8855,
gcd(91586, 8855) = 253 first time.
		

Crossrefs

Cf. A007053, A000720, A087266-A087269, A057809.

Programs

Mathematica

f[x_] := GCD[x, PrimePi[x]]; t=Table[0, {257}]; Do[s=f[n]; If[s<258&&t[[s]]==0, t[[s]]=n], {n, 1, 100000}]; t
Module[{tbl=Table[{x,GCD[x,PrimePi[x]]},{x,12000}]},Table[SelectFirst[ tbl,#[[2]]==n&],{n,50}]][[All,1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Feb 12 2020 *)

Formula

a(n) = Min{x; gcd(x, A000720(x))=n}.