A218466 - OEIS

%I #20 Apr 09 2013 19:29:56

%S 5,10,27,17,25,54,23,34,61,47,55,108,47,46,139,68,58,122,71,85,144,95,

%T 115,207,101,94,183,92,145,278,104,136,177,116,175,244,161,142,306,

%U 149,184,283,191,187,410,230,235,267,146,202,299,188,157,366,275,184

%N Least k > n for which phi(k - n) = phi(k + n) or 0 if no such k exists.

%C Is there an upper bound for a(n) for a given n? - _Michael B. Porter_, Apr 06 2013

%H Donovan Johnson, <a href="/A218466/b218466.txt">Table of n, a(n) for n = 1..1000</a>

%e a(3) = 27 since phi(27 - 3) = phi(24) = 8 and phi(27 + 3) = phi(30) = 8, and 27 is the smallest number greater than 3 for which the two are equal.

%o (PARI) /* will not terminate if k does not exist */

%o a218446(n) = {local(k); k = n + 1; while(eulerphi(k - n) <> eulerphi(k + n), k = k + 1); k} \\ _Michael B. Porter_, Mar 30 2013

%Y Cf. A000010, A217768, A223091.

%K nonn

%O 1,1

%A _Irina Gerasimova_, Mar 26 2013

%E Extended by _R. J. Mathar_, Mar 27 2013