cp's OEIS Frontend

A046635 Number of cubic residues mod 7^n.

%I A046635 #17 Nov 24 2017 16:32:04
%S A046635 1,3,15,99,689,4817,33713,235987,1651903,11563315,80943201,566602401,
%T A046635 3966216801,27763517603,194344623215,1360412362499,9522886537489,
%U A046635 66660205762417,466621440336913,3266350082358387,22864450576508703
%N A046635 Number of cubic residues mod 7^n.
%H A046635 S. R. Finch and Pascal Sebah, <a href="http://arXiv.org/abs/math.NT/0604465">Squares and Cubes Modulo n</a> (arXiv:math.NT/0604465).
%H A046635 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (7,0,1,-7).
%F A046635 a(n) = A046530(7^n).
%F A046635 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
%p A046635 A046635 := proc(n)
%p A046635     7^(n+2)+2*op(1+modp(n,3),[61,85,82]) ;
%p A046635     %/171 ;
%p A046635 end proc:
%p A046635 seq(A046635(n),n=0..20) ; # _R. J. Mathar_, Oct 08 2017
%t A046635 LinearRecurrence[{7, 0, 1, -7}, {1, 3, 15, 99}, 21] (* _Jean-François Alcover_, Nov 24 2017 *)
%K A046635 nonn,easy
%O A046635 0,2
%A A046635 _David W. Wilson_