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 A046635 Number of cubic residues mod 7^n. 2

%I

%S 1,3,15,99,689,4817,33713,235987,1651903,11563315,80943201,566602401,

%T 3966216801,27763517603,194344623215,1360412362499,9522886537489,

%U 66660205762417,466621440336913,3266350082358387,22864450576508703

%N Number of cubic residues mod 7^n.

%H 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 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (7,0,1,-7).

%F a(n) = A046530(7^n).

%F 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 := proc(n)

%p 7^(n+2)+2*op(1+modp(n,3),[61,85,82]) ;

%p %/171 ;

%p end proc:

%p seq(A046635(n),n=0..20) ; # _R. J. Mathar_, Oct 08 2017

%t LinearRecurrence[{7, 0, 1, -7}, {1, 3, 15, 99}, 21] (* _Jean-François Alcover_, Nov 24 2017 *)

%K nonn,easy

%O 0,2

%A _David W. Wilson_

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Last modified August 6 12:33 EDT 2020. Contains 336246 sequences. (Running on oeis4.)