cp's OEIS Frontend

A074625 Triangular array T(n,k) (n >= 1, 1 <= k <= n) read by rows, where T(n,k) = smallest number x such that Mod[sigma[x],n]=k.

%I A074625 #11 Dec 19 2013 03:28:23
%S A074625 1,1,3,1,7,2,1,5,2,3,1,4,2,3,8,1,7,2,3,2401,5,1,29,2,3,6,5,4,1,10,2,3,
%T A074625 9,5,4,7,1,19,2,3,13,5,4,7,10,1,6,2,3,8,5,4,7,18,19,1,9,2,3,24,5,4,7,
%U A074625 16,21,43,1,13,2,3,2401,5,4,7,49,31213,9604,6,1,8,2,3,10,5,4,7,33,22
%N A074625 Triangular array T(n,k) (n >= 1, 1 <= k <= n) read by rows, where T(n,k) = smallest number x such that Mod[sigma[x],n]=k.
%C A074625 In the table output, one can observe constant diagonals (or lines in the square output). The indices of these are: 1, 3, 4, 6, 7, 8, 12, 13, ... (see A002191). And the corresponding values are: 1, 2, 3, 5, 4, 7, 6, 9, ... (see A002192). - _Michel Marcus_, Dec 19 2013
%F A074625 Min{x; Mod[sigma[x], n]=r}, r=1..n, n=1, ...
%e A074625 Triangle begins
%e A074625 1;
%e A074625 1,3;
%e A074625 1,7,2;
%e A074625 1,5,2,3;
%e A074625 1,4,2,3,8; ...
%t A074625 {k=0, s=0, fl=1}; Table[Print["#"]; Table[fl=1; Print[{r, m}]; Do[s=Mod[DivisorSigma[1, n], m]; If[(s==r)&&(fl==1), Print[n]; fl=0], {n, 1, 150000}], {r, 0, m-1}], {m, 1, 25}]
%Y A074625 Cf. A000203, A028982, A074384, A074386, A072461, A072462, A072862.
%K A074625 nonn,tabl
%O A074625 1,3
%A A074625 _Labos Elemer_, Aug 26 2002