A275800 - OEIS

%I #7 Aug 09 2016 17:16:16

%S 5,13,17,139,173,179,467,907,1553,1619,1867,2099,2819,2957,3203,3779,

%T 3947,4139,4157,4283,4547,4723,5483,6653,6899,7013,7187,7523,7643,

%U 8147,8387,8563,8573,8753,9533,9587,10589,10853,10883,10979,11003,12107,12227,13037,13229,13829,14243,14549,14699,14867,15299,16217,16547,16649,17387,18443,18587,19259

%N n such that A275391(n) = n-2.

%C n such that n-2 is the least k such that n divides A062727(k) = sigma(k^k).

%C Are all terms prime?

%e 17 is in the sequence because 17 divides sigma(15^15) = 821051025385244160 but does not divide sigma(k^k) for any k < 15.

%p N:= 20000:

%p S:= {$1..N}: # to get terms <= N

%p for kk from 1 while S <> {} do

%p    v:= numtheory:-sigma(kk^kk);

%p    F:= select(t -> v mod t = 0, S);

%p    for nn in F do

%p      B[nn]:= kk

%p    od;

%p    S:= S minus F;

%p od:

%p select(t -> B[t]=t-2, [$1..N]);

%Y Cf. A000203, A062727, A275391.

%K nonn

%O 1,1

%A _Robert Israel_, Aug 09 2016