A344308 - OEIS

%I #15 May 19 2021 02:13:56

%S 1,2,3,5,6,7,10,13,14,15,17,19,21,23,26,29,30,34,35,37,38,39,42,43,46,

%T 47,51,53,57,58,59,65,67,69,70,73,74,78,79,83,85,86,87,89,91,94,95,97,

%U 102,103,105,106,107,109,111,113,114,115,118,119,127,129,130,133,134,137,138,139,141,145

%N Numbers k such that A205791(k) = k+1.

%H Robert Israel, <a href="/A344308/b344308.txt">Table of n, a(n) for n = 1..1258</a>

%e a(6) = 7 is a term because A205791(7) = 8.

%p N:= 200: # for terms <= N

%p V:= Vector(N):

%p count:= 0:

%p for k from 1 while count < N do

%p   for j from 1 to k-1 while count < N do

%p     Q:= select(t -> t <= N and V[t] = 0, numtheory:-divisors(k^5-j^5));

%p     if Q <> {} then

%p        newcount:= nops(Q);

%p        count:= count + newcount;

%p        V[convert(Q, list)]:= k;

%p     fi

%p od od:

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

%t Select[Range@200,(k=1;While[FreeQ[Mod[Table[k^5-j^5,{j,k-1}],#],0],k++];k)==#+1&] (* _Giorgos Kalogeropoulos_, May 14 2021 *)

%Y Cf. A205791.

%Y Subset of A005117.

%K nonn

%O 1,2

%A _Robert Israel_, May 14 2021