OFFSET
0,3
COMMENTS
Number of ways to assign truth values to n ternary conjunctions connected by disjunctions such that the proposition is true. For example, a(2) = 15, since for the proposition '(a & b & c) v (d & e & f)' there are 15 assignments that make the proposition true. - Ori Milstein, Dec 22 2022
Equivalently, the number of length-n words over the alphabet {0,1,...,7} with at least one letter = 7. - Joerg Arndt, Jan 01 2023
a(n) is also the number of n-digit numbers whose smallest decimal digit is 2. - Stefano Spezia, Nov 15 2023
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (15,-56).
FORMULA
G.f.: x/((1-7x)*(1-8x)).
a(n) = numerator(f(n-1)) where f(n) = Integral_{x=0..1/4} (1-x/2)^n dx. And denominator(f(n)) = 4*(n+1)*8^n. - Al Hakanson (hawkuu(AT)excite.com), Feb 22 2004 [corrected by Michel Marcus, Dec 23 2022]
a(n) = 15*a(n-1) - 56*a(n-2), n > 1. - Philippe Deléham, Jan 01 2009
E.g.f.: e^(8*x) - e^(7*x). - Mohammad K. Azarian, Jan 14 2009
a(n) = 8*a(n-1) + 7^(n-1), a(0)=0. - Vincenzo Librandi, Feb 09 2011
MATHEMATICA
Table[8^n - 7^n, {n, 0, 20}] (* Harvey P. Dale, Jan 31 2011 *)
PROG
(PARI) a(n)=8^n-7^n \\ Charles R Greathouse IV, Sep 28 2015
(Magma) [8^n -7^n: n in [0..40]]; // G. C. Greubel, Nov 29 2024
(Python)
def A016177(n): return pow(8, n) - pow(7, n)
print([A016177(n) for n in range(41)]) # G. C. Greubel, Nov 29 2024
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved