OFFSET
0,2
COMMENTS
Apparently a(9+n) = A194519(n).
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,0,0,0,0,1,-1).
FORMULA
Conjecture: a(n)= +a(n-1) +a(n-10) -a(n-11) with G.f. x*(-2 +x -2*x^3 +x^4 -2*x^6 +x^7 +x^9 +x^2 +x^5 +x^8) / ( (1+x) *(x^4+x^3+x^2+x+1) *(x^4-x^3+x^2-x+1) *(x-1)^2 ). - R. J. Mathar, Oct 04 2011
The conjecture above is correct. - Charles R Greathouse IV, Jan 04 2013
EXAMPLE
Check to see if 273 is divisible by 7 : double the last digit 3*2=6 ; subtract that from the rest of the number 27-6=21 ; check to see if the difference is divisible by 7: 21/7 is divisible by 7, therefore 273 is also divisible by 7. 273=7*39 and 21=7*3 so a(39)=3.
MAPLE
A196279 := proc(n)
r := (7*n) mod 10 ;
x := floor(7*n/10) ;
(x-2*r)/7 ;
end proc: # R. J. Mathar, Oct 04 2011
PROG
(PARI) a(n)=(7*n\10-7*n%10*2)/7 \\ Charles R Greathouse IV, Jan 04 2013
CROSSREFS
KEYWORD
sign,base,easy
AUTHOR
Philippe Deléham, Sep 30 2011
STATUS
approved
