OFFSET
0,10
COMMENTS
The first difference between the entries in row r is r.
Partial sums of floor(n/8). - Philippe Deléham, Mar 26 2013
Apart from the initial zeros, the same as A008726. - Philippe Deléham, Mar 28 2013
a(n+7) is the number of key presses required to type a word of n letters, all different, on a keypad with 8 keys where 1 press of a key is some letter, 2 presses is some other letter, etc., and under an optimal mapping of letters to keys and presses (answering LeetCode problem 3014). - Christopher J. Thomas, Feb 16 2024
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,0,0,0,1,-2,1).
FORMULA
From Philippe Deléham, Mar 26 2013: (Start)
a(8k) = A001107(k).
a(8k+1) = A002939(k).
a(8k+2) = A033991(k).
a(8k+3) = A016742(k).
a(8k+4) = A007742(k).
a(8k+5) = A002943(k).
a(8k+6) = A033954(k).
a(8k+7) = A033996(k). (End)
G.f.: x^8/((1-x)^2*(1-x^8)). - Philippe Deléham, Mar 28 2013
a(n) = floor(n/8)*(n-3-4*floor(n/8)). - Ridouane Oudra, Jun 04 2019
a(n+7) = (1/2)*(n+(n mod 8))*(floor(n/8)+1). - Christopher J. Thomas, Feb 13 2024
EXAMPLE
The array starts, with row r=0, as
r=0: 0 0 0 0 0 0 0 0;
r=1: 1 2 3 4 5 6 7 8;
r=2: 10 12 14 16 18 20 22 24;
r=3: 27 30 33 36 39 42 45 48;
MATHEMATICA
Flatten[Table[4r^2+r(Range[-3, 4]), {r, 0, 6}]] (* or *) LinearRecurrence[ {2, -1, 0, 0, 0, 0, 0, 1, -2, 1}, {0, 0, 0, 0, 0, 0, 0, 0, 1, 2}, 60] (* Harvey P. Dale, Nov 26 2015 *)
CROSSREFS
KEYWORD
nonn,tabf,easy
AUTHOR
Stuart M. Ellerstein (ellerstein(AT)aol.com), May 21 2006
EXTENSIONS
Redefined as a rectangular tabf array and description simplified by R. J. Mathar, Oct 20 2010
STATUS
approved