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 A062204 Number of alignments of n strings of length 7. 4
 1, 1, 48639, 75494983297, 1177359342144641535, 103746115308050354021387521, 36585008462723983824862891403150079, 41020870889694863957061607086939138327565057, 124069835911824710311393852646151897334844371419287295 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Strings of length 7 represent the average word length for most natural languages such as English. This sequence represents the search space for alignment and sequencing algorithms that work on multiple sets of strings. The assertion that "strings of length 7 represent the average word length for most natural languages such as English" seems to conflict with studies that show that the average word length in English is about 4.5 letters and the average word length in modern Russian is 5.28 letters. - M. F. Hasler, Mar 12 2009 In general, row r > 0 of A262809 is asymptotic to sqrt(r*Pi) * (r^(r-1)/(r-1)!)^n * n^(r*n+1/2) / (2^(r/2) * exp(r*n) * (log(2))^(r*n+1)). - Vaclav Kotesovec, Mar 23 2016 REFERENCES M. S. Waterman, Introduction to Computational Biology: Maps, Sequences and Genomes, 1995. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..50 M. A. Covington, The number of distinct alignments of two strings, Journal of Quantitative Linguistics, Volume 11, no. 3 (2004), 173-182. Michael S. Waterman, Home Page (contains copies of his papers) FORMULA A(n, y) = sum(k=0,n*y, sum(t=0,k, (-1)^t * binomial(k,t) * binomial(k-t,y)^n )). a(n) ~ sqrt(7*Pi) * (7^6/6!)^n * n^(7*n+1/2) / (2^(7/2) * exp(7*n) * (log(2))^(7*n+1)). - Vaclav Kotesovec, Mar 23 2016 EXAMPLE A(2, 7) = 48639 since this represents the number of distinct alignments of 2 strings of length 7. All values in A(2,X) can be cross-validated against the Delannoy sequence D(X,X) A001850. MATHEMATICA With[{r = 7}, Flatten[{1, Table[Sum[Sum[(-1)^i*Binomial[j, i]*Binomial[j - i, r]^k, {i, 0, j}], {j, 0, k*r}], {k, 1, 10}]}]] (* Vaclav Kotesovec, Mar 22 2016 *) CROSSREFS Cf. A062205, A062208, A001850. A(2, X) represents Waterman's f function. Row n=7 of A262809. Sequence in context: A244172 A245794 A048341 * A173780 A252444 A237146 Adjacent sequences:  A062201 A062202 A062203 * A062205 A062206 A062207 KEYWORD nonn AUTHOR Angelo Dalli, Jun 13 2001 EXTENSIONS Formula and sequence revised by Max Alekseyev, Mar 12 2009 STATUS approved

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