

A328918


a(n) is the number of ordered pairs of positive integers (x, y) with x + y = 10^n, where x and y each have exactly ndigits but with initial zero digits allowed, and as strings, x and y are permutations of each other.


0



1, 1, 11, 11, 281, 281, 11181, 11181, 563131, 563131, 32795191, 32795191, 2103687091, 2103687091, 144420919291, 144420919291, 10421915468041, 10421915468041, 781300466839541, 781300466839541, 60358948031151561, 60358948031151561, 4777791013174712961
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OFFSET

1,3


COMMENTS

Published with slightly different wording in Mathematics Magazine, Problem 1016, Dec. 1977.
Analyzed for n = 1, 2, 3; computerverified for n up to 8.
All solutions consist of an even number of digits followed by the digit 5 followed by zero or more 0's. This pattern means that a(2*n1) = a(2*n). The initial segment consists of pairs of digits that add to 9 (0 with 9, 1 with 8, etc) arranged in arbitrary order and in particular leading 0's are permitted by the definition of the problem. A287317(k) gives the number of such arrangement with k pairs. For example, 339606500 + 660393500 is a solution.  Andrew Howroyd, Nov 03 2019


LINKS

Michael W. Ecker, Problem 1016, Mathematics Magazine, Vol. 50, No. 3 (May, 1977), pp. 163169.


FORMULA



EXAMPLE

For n = 3, solutions are (095, 905), (185, 815), (275, 725), (365, 635), (455, 545), (500, 500), (545, 455), (635, 365), (725, 275), (815, 185), (905, 095).


PROG

(PARI) seq(n)={Vec(serlaplace(besseli(0, 2*x + O(x*x^n))^5)/(1x))} \\ Andrew Howroyd, Nov 03 2019


CROSSREFS



KEYWORD

nonn,base


AUTHOR



EXTENSIONS



STATUS

approved



