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A324924 Irregular triangle read by rows giving the factorization of n into factors q(i) = prime(i)/i, i > 0. 27
1, 1, 2, 1, 1, 1, 2, 3, 1, 1, 2, 1, 1, 4, 1, 1, 1, 1, 1, 2, 2, 1, 1, 2, 3, 1, 2, 3, 5, 1, 1, 1, 2, 1, 1, 2, 6, 1, 1, 1, 4, 1, 1, 2, 2, 3, 1, 1, 1, 1, 1, 1, 4, 7, 1, 1, 1, 2, 2, 1, 1, 1, 8, 1, 1, 1, 2, 3, 1, 1, 1, 2, 4, 1, 1, 2, 3, 5, 1, 1, 2, 2, 9 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Row n is the multiset of Matula-Goebel numbers of all proper terminal subtrees of the rooted tree with Matula-Goebel number n. For example, the rooted tree with Matula-Goebel number 1362 is (o(o)((oo)(oo))), with proper terminal subtrees {o,o,o,o,o,o,(o),(oo),(oo),((oo)(oo))}, which have Matula-Goebel numbers {1,1,1,1,1,1,2,4,4,49}, which is row 1362, as required.

LINKS

Table of n, a(n) for n=1..83.

EXAMPLE

Triangle begins:

  {}

  1

  1  2

  1  1

  1  2  3

  1  1  2

  1  1  4

  1  1  1

  1  1  2  2

  1  1  2  3

  1  2  3  5

  1  1  1  2

  1  1  2  6

  1  1  1  4

  1  1  2  2  3

  1  1  1  1

  1  1  4  7

  1  1  1  2  2

  1  1  1  8

  1  1  1  2  3

  1  1  1  2  4

  1  1  2  3  5

  1  1  2  2  9

For example, row 65 is {1,1,1,2,2,3,6} because 65 = q(1)^3 q(2)^2 q(3) q(6).

MATHEMATICA

difac[n_]:=If[n==1, {}, With[{i=PrimePi[FactorInteger[n][[1, 1]]]}, Sort[Prepend[difac[n*i/Prime[i]], i]]]];

Table[difac[n], {n, 30}]

CROSSREFS

Cf. A000081, A003963, A061775, A109082, A109129, A112798, A120383, A196050, A317713, A324850, A324922, A324923, A324925, A324931, A324934.

Sequence in context: A308993 A000188 A162401 * A301314 A241898 A191090

Adjacent sequences:  A324921 A324922 A324923 * A324925 A324926 A324927

KEYWORD

nonn,tabf

AUTHOR

Gus Wiseman, Mar 20 2019

STATUS

approved

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Last modified December 8 12:07 EST 2019. Contains 329862 sequences. (Running on oeis4.)