A121920 - OEIS

%I #12 Nov 01 2019 15:46:51

%S 1,4,9,8,25,10,49,16,27,18,121,22,169,26,36,32,289,34,361,38,54,42,

%T 529,46,125,50,81,54,841,63,961,64,88,66,120,70,1369,74,105,78,1681,

%U 87,1849,86,111,90,2209,94,343,98,141,102,2809,106,210,110,159,114,3481,125

%N a(n) = n-th integer from among those positive integers k where GCD(k,n) = prime power >1. a(1) = 1.

%e 2,4,5,6,8,12,14,15,16,18,22,... is the sequence of positive integers k where GCD(k, 10) = p^j, j = positive integer, p = prime. 18 is the 10th of these integers, so a(10) = 18.

%t f[n_] := Block[{c = n, k = 0},If[n == 1, 1, While[c > 0,k++; While[Length[FactorInteger[GCD[k, n]]] != 1, k++ ]; c--;];k]]; Table[f[n], {n, 65}] (* _Ray Chandler_, Sep 06 2006 *)

%K nonn

%O 1,2

%A _Leroy Quet_, Sep 02 2006

%E Extended by _Ray Chandler_, Sep 06 2006