login
A046635
Number of cubic residues mod 7^n.
2
1, 3, 15, 99, 689, 4817, 33713, 235987, 1651903, 11563315, 80943201, 566602401, 3966216801, 27763517603, 194344623215, 1360412362499, 9522886537489, 66660205762417, 466621440336913, 3266350082358387, 22864450576508703
OFFSET
0,2
LINKS
S. R. Finch and Pascal Sebah, Squares and Cubes Modulo n (arXiv:math.NT/0604465).
FORMULA
a(n) = A046530(7^n).
a(n)= +7*a(n-1) +a(n-3) -7*a(n-4) with g.f. ( 1-4*x-6*x^2-7*x^3 ) / ( (x-1)*(7*x-1)*(1+x+x^2) ). - R. J. Mathar, Feb 27 2011
MAPLE
A046635 := proc(n)
7^(n+2)+2*op(1+modp(n, 3), [61, 85, 82]) ;
%/171 ;
end proc:
seq(A046635(n), n=0..20) ; # R. J. Mathar, Oct 08 2017
MATHEMATICA
LinearRecurrence[{7, 0, 1, -7}, {1, 3, 15, 99}, 21] (* Jean-François Alcover, Nov 24 2017 *)
CROSSREFS
Sequence in context: A186264 A140286 A199416 * A208426 A168344 A091713
KEYWORD
nonn,easy
STATUS
approved