A256440 - OEIS

%I #15 Dec 22 2017 08:46:13

%S 1,1,2,1,3,2,1,3,2,4,1,5,3,2,4,1,5,3,2,4,6,1,7,5,3,2,4,6,1,7,5,3,2,4,

%T 8,6,1,7,5,3,9,2,4,8,6,1,7,5,3,9,2,4,10,8,6,1,11,7,5,3,9,2,4,10,8,6,1,

%U 11,7,5,3,9,2,4,10,8,6,12,1,13,11,7,5,3,9,2,4,10,8,6,12

%N Regular triangle where the n-th row lists the integers k between 1 and n ordered by increasing value of sigma(k)/k where sigma is the sum of divisors, A000203.

%H Michel Marcus, <a href="/A256440/b256440.txt">Rows n = 1..100 of triangle, flattened</a>

%H Michel Marcus, <a href="/A256440/a256440.txt">100 rows</a>

%e Triangle starts:

%e 1;

%e 1, 2;

%e 1, 3, 2;

%e 1, 3, 2, 4;

%e 1, 5, 3, 2, 4;

%e 1, 5, 3, 2, 4, 6;

%e 1, 7, 5, 3, 2, 4, 6;

%e ...

%t f[n_] := Block[{t = Table[0, {n}], j, k}, For[j = 1, j <= n, j++, t[[j]] = {}; For[k = 1, k <= j, k++, AppendTo[t[[j]], DivisorSigma[1, k]/k]]]; Ordering /@ t]; f@ 13 // Flatten (* _Michael De Vlieger_, Mar 29 2015 *)

%o (PARI) lista(nn) = {for (n=1, nn, v = vector(n, k, sigma(k)/k); w = vecsort(v,,1); for (k=1, n, print1(w[k], ", ")); print(););}

%Y Cf. A000203, A247015, A247022.

%K nonn,tabl

%O 1,3

%A _Michel Marcus_, Mar 29 2015