A350317 - OEIS

%I #13 Oct 01 2023 13:59:07

%S 1,10,18,46,58,70,78,82,102,106,110,130,136,148,166,178,190,220,222,

%T 226,238,250,262,268,270,282,292,310,316,330,342,346,358,378,382,418,

%U 430,438,442,466,478,486,490,498,502,508,522,556,562,568,586,598,606,618

%N Totient numbers k such that 5*k is a nontotient.

%H Winston de Greef, <a href="/A350317/b350317.txt">Table of n, a(n) for n = 1..10000</a>

%e 10 is a term since 10 = phi(11) = phi(22), but phi(n) = 5*10 = 50 has no solution.

%e 18 is a term since 18 = phi(19) = phi(27) = phi(38) = phi(54), but phi(n) = 5*18 = 90 has no solution.

%o (PARI) isA350317(n) = istotient(n) && !istotient(5*n)

%Y Totient numbers k such that m*k is a nontotient: A350316 (m=3), this sequence (m=5), A350318 (m=7), A350319 (m=9), A350320 (m=10), A350321 (m=14).

%Y Cf. A002202, A005277.

%K nonn

%O 1,2

%A _Jianing Song_, Dec 24 2021