cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A273978 List of words of length n over an alphabet of size 9 that are in standard order and which have the property that every letter that appears in the word is repeated.

Original entry on oeis.org

11, 111, 1111, 1122, 1212, 1221, 11111, 11122, 11212, 11221, 11222, 12112, 12121, 12122, 12211, 12212, 12221, 111111, 111122, 111212, 111221, 111222, 112112
Offset: 1

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Author

Keywords

Comments

We study words made of letters from an alphabet of size b, where b >= 1. (Here b=9.) We assume the letters are labeled {1,2,3,...,b}. There are b^n possible words of length n.
We say that a word is in "standard order" if it has the property that whenever a letter i appears, the letter i-1 has already appeared in the word. This implies that all words begin with the letter 1.
These are the words described in row b=9 of the array in A278987.

References

  • D. D. Hromada, Integer-based nomenclature for the ecosystem of repetitive expressions in complete works of William Shakespeare, submitted to special issue of Argument and Computation on Rhetorical Figures in Computational Argument Studies, 2016.

Crossrefs

Subset of A273977.
Cf. A278987.

Extensions

Edited by N. J. A. Sloane, Dec 06 2016

A278986 Array read by antidiagonals downwards: T(b,n) = number of words of length n over an alphabet of size b that are in standard order and which have the property that at least one letter is repeated.

Original entry on oeis.org

0, 1, 0, 1, 1, 0, 1, 4, 1, 0, 1, 8, 4, 1, 0, 1, 16, 14, 4, 1, 0, 1, 32, 41, 14, 4, 1, 0, 1, 64, 122, 51, 14, 4, 1, 0, 1, 128, 365, 187, 51, 14, 4, 1, 0, 1, 256, 1094, 715, 202, 51, 14, 4, 1, 0, 1, 512, 3281, 2795, 855, 202, 51, 14, 4, 1, 0, 1, 1024, 9842, 11051, 3845, 876, 202, 51, 14, 4, 1
Offset: 1

Views

Author

Joerg Arndt and N. J. A. Sloane, Dec 05 2016

Keywords

Comments

We study words made of letters from an alphabet of size b, where b >= 1. We assume the letters are labeled {1,2,3,...,b}. There are b^n possible words of length n.
We say that a word is in "standard order" if it has the property that whenever a letter i appears, the letter i-1 has already appeared in the word. This implies that all words begin with the letter 1.

Examples

			The array begins:
0,.1,..1,...1,...1,...1,...1,....1..; b=1,
0,.1,..4,...8,..16,..32,..64,..128..; b=2,
0,.1,..4,..14,..41,.122,.365,.1094..; b=3,
0,.1,..4,..14,..51,.187,.715,.2795..; b=4,
0,.1,..4,..14,..51,.202,.855,.3845..; b=5,
0,.1,..4,..14,..51,.202,.876,.4111..; b=6,
...
		

Crossrefs

See A278984 for a closely related array.
The words for b=3 are listed in A278985, except that the words 1, 12, and 123 must be omitted from that list.
The words for b=9 are listed in A273977.

Programs

  • Maple
    with(combinat);
    f2:=proc(L,b) local t1;i;
    t1:=add(stirling2(L,i),i=1..b); if L <= b then t1:=t1-1; fi; t1; end;
    Q2:=b->[seq(f2(L,b), L=1..20)];
    for b from 1 to 6 do lprint(Q2(b)); od:

Formula

The number of words of length n over an alphabet of size b that are in standard order and in which at least one symbol is repeated is Sum_{j = 1..b} Stirling2(n,j), except we must subtract 1 if and only if n <= b.
So this array is obtained from the array in A278984 by subtracting 1 from the first b entries in row b, for b = 1,2,3,...
Showing 1-2 of 2 results.