OFFSET
0,2
COMMENTS
Number of distinct n-digit numbers up to permutations of digits. - Michael Somos, Jul 11 2002
Equivalently, for n > 0, a(n) = number of n-digit decimal numbers d_1 d_2 ... d_n with d_1 > 0 and d_1 >= d_2 >= ... >= d_n >= 0.. - N. J. A. Sloane, Jul 13 2023
LINKS
Michael Beeler, R. William Gosper and Richard C. Schroeppel, HAKMEM, ITEM 56, Cambridge, MA: Mass. Institute of Technology Artificial Intelligence Laboratory, Memo AIM-239, Feb. 1972, Item 56.
Eric Weisstein's World of Mathematics, Multiplicative Persistence.
Index entries for linear recurrences with constant coefficients, signature (10,-45,120,-210,252,-210,120,-45,10,-1).
FORMULA
G.f.: 1/(1-x)^10-1/(1-x). - Michael Somos, Jul 11 2002
MAPLE
binomial(10+n-1, n)-1;
MATHEMATICA
Table[Binomial[9 + n, n] - 1, {n, 0, 27}] (* Michael De Vlieger, Jul 14 2015 *)
CoefficientList[Series[1/(1-x)^10-1/(1-x), {x, 0, 30}], x] (* or *) LinearRecurrence[{10, -45, 120, -210, 252, -210, 120, -45, 10, -1}, {0, 9, 54, 219, 714, 2001, 5004, 11439, 24309, 48619}, 30] (* Harvey P. Dale, Jul 11 2023 *)
PROG
(PARI) a(n)=if(n<0, 0, binomial(n+9, 9)-1)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved