A393065 - OEIS

A393065

Numbers k such that A020639(k') = A053669(k) and A053669(k') = A020639(k), where k' stands for the arithmetic derivative of k, A020639 returns the least prime factor of its argument, and A053669 is the least prime not dividing its argument.

%I #11 Jan 31 2026 23:23:06

%S 1,6,14,15,21,26,33,35,38,39,50,51,57,62,65,69,74,86,87,93,95,110,111,

%T 122,123,129,134,141,146,155,158,159,161,170,177,183,185,194,201,206,

%U 213,215,218,219,230,237,242,249,254,267,278,290,291,302,303,305,309,314,321,326,327,330,335,339,362,365,371,374

%N Numbers k such that A020639(k') = A053669(k) and A053669(k') = A020639(k), where k' stands for the arithmetic derivative of k, A020639 returns the least prime factor of its argument, and A053669 is the least prime not dividing its argument.

%H Antti Karttunen, <a href="/A393065/b393065.txt">Table of n, a(n) for n = 1..20000</a>

%F {k such that A020639(A003415(k)) == A053669(k) and A053669(A003415(k)) == A020639(k)}.

%o (PARI) is_A393065 = A393064;

%Y Intersection of A370125 and A391845.

%Y Cf. A003415, A020639, A053669, A393064 (characteristic function).

%Y Subsequence: A393066 (terms k such that k+1 is also a term).

%K nonn,easy

%O 1,2

%A _Antti Karttunen_, Jan 31 2026