A254679 Irregular triangle read by rows: row n lists the divisors of n, ordered lexicographically in decimal representation.

1, 1, 2, 1, 3, 1, 2, 4, 1, 5, 1, 2, 3, 6, 1, 7, 1, 2, 4, 8, 1, 3, 9, 1, 10, 2, 5, 1, 11, 1, 12, 2, 3, 4, 6, 1, 13, 1, 14, 2, 7, 1, 15, 3, 5, 1, 16, 2, 4, 8, 1, 17, 1, 18, 2, 3, 6, 9, 1, 19, 1, 10, 2, 20, 4, 5, 1, 21, 3, 7, 1, 11, 2, 22, 1, 23, 1, 12, 2, 24

Offset

1,3

Links

Reinhard Zumkeller, Rows n = 1..1000 of triangle, flattened

Example

.    n | T(n,1..A000005(n))       n | T(n,1..A000005(n))
.  ----+-------------------     ----+-------------------
.    1 | 1                       21 | 1 21 3 7
.    2 | 1 2                     22 | 1 11 2 22
.    3 | 1 3                     23 | 1 23
.    4 | 1 2 4                   24 | 1 12 2 24 3 4 6 8
.    5 | 1 5                     25 | 1 25 5
.    6 | 1 2 3 6                 26 | 1 13 2 26
.    7 | 1 7                     27 | 1 27 3 9
.    8 | 1 2 4 8                 28 | 1 14 2 28 4 7
.    9 | 1 3 9                   29 | 1 29
.   10 | 1 10 2 5                30 | 1 10 15 2 3 30 5 6
.   11 | 1 11                    31 | 1 31
.   12 | 1 12 2 3 4 6            32 | 1 16 2 32 4 8
.   13 | 1 13                    33 | 1 11 3 33
.   14 | 1 14 2 7                34 | 1 17 2 34
.   15 | 1 15 3 5                35 | 1 35 5 7
.   16 | 1 16 2 4 8              36 | 1 12 18 2 3 36 4 6 9
.   17 | 1 17                    37 | 1 37
.   18 | 1 18 2 3 6 9            38 | 1 19 2 38
.   19 | 1 19                    39 | 1 13 3 39
.   20 | 1 10 2 20 4 5           40 | 1 10 2 20 4 40 5 8 .

Prog

(Haskell)
import Data.List (sortBy); import Data.Ord (comparing)
a254679 n k = a254679_tabf !! (n-1) !! (k-1)
a254679_row n = a254679_tabf !! (n-1)
a254679_tabf = map (sortBy (comparing show)) a027750_tabf
(PARI) cmps(x, y) = cmp(Str(x), Str(y));
row(n) = vecsort(divisors(n), cmps); \\ Michel Marcus, Jan 23 2022

Crossrefs

Cf. A027750, A000005 (row lengths), A000203 (row sums), A122425 (right edge).

Sequence in context: A233773 A027750 A275055 * A343651 A355634 A275280

Adjacent sequences: A254676 A254677 A254678 * A254680 A254681 A254682

Keyword

nonn,base,tabf

Author

Reinhard Zumkeller, Feb 05 2015

Status

approved