A240597 - OEIS

%I #36 Feb 09 2021 01:57:08

%S 1,15,24,42,60,64,69,78,90,100,114,123,133,147,153,177,186,198,222,

%T 231,240,258,259,270,276,288,289,306,339,360,366,393,402,403,414,429,

%U 438,447,459,474,477,492,495,501,507,511,522,582,588,594,600

%N Numbers k such that sigma(k) == k (mod 9).

%C That is, numbers k that satisfy the following:

%C A010878(k) = A105852(k) or A010878(k) = A010878(A000203(k)).

%C A010888(k) = A190998(k) or A010888(k) = A010888(A000203(k)).

%H Ivan N. Ianakiev, <a href="/A240597/b240597.txt">Table of n, a(n) for n = 1..10000</a>

%F A010888(a(n)) = A010888(A000203(a(n))).

%F A010888(a(n)) = A190998(a(n)).

%e sigma(15) = 24. 24 == 15 (mod 9), therefore 15 is in the sequence.

%t Select[Range[1000],Mod[#,9]==Mod[DivisorSigma[1,#],9]&]

%Y Cf. A000203, A190998, A010878, A105852, A010888.

%K easy,nonn

%O 1,2

%A _Ivan N. Ianakiev_, Sep 13 2014