A227429 - OEIS

%I #15 Nov 28 2021 11:50:37

%S 1,3,4,12,21,39,91,156,381,1668,3292,4541,6515,12927,49492,72412,

%T 100595,158708

%N Numbers k such that Sum_{j=1..k} j^phi(j) == 0 (mod k).

%C a(17) > 10^5. - _Giovanni Resta_, Jul 11 2013

%C a(19) > 2473000. - _Kevin P. Thompson_, Nov 28 2021

%e 4 is a member of the sequence since Sum_{j=1..4} j^phi(j) = 1^phi(1) + 2^phi(2) + 3^phi(3) + 4^phi(4) = 1^1 + 2^1 + 3^2 + 4^2 = 28 which is divisible by 4.

%p with(numtheory); ListA227429:=proc(q) local i,n;

%p for n from 1 to q do if add(i^phi(i),i=1..n) mod n=0 then print(n);

%p fi; od; end: ListA227429(10^6);

%Y Cf. A000010, A227427.

%K nonn,more

%O 1,2

%A _Paolo P. Lava_, Jul 11 2013

%E a(10)-a(16) from _Giovanni Resta_, Jul 11 2013

%E a(17)-a(18) from _Kevin P. Thompson_, Nov 28 2021