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a(n) = n^7 - n^6.
4

%I #31 Sep 08 2022 08:46:07

%S 0,0,64,1458,12288,62500,233280,705894,1835008,4251528,9000000,

%T 17715610,32845824,57921708,97883968,159468750,251658240,386201104,

%U 578207808,846825858,1216000000,1715322420,2380977984,3256789558,4395368448,5859375000,7722894400,10072932714

%N a(n) = n^7 - n^6.

%C For n>1 number of 7-digit positive integers in base n.

%H Vincenzo Librandi, <a href="/A240930/b240930.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (8,-28,56,-70,56,-28,8,-1).

%F a(n) = n^6*(n-1) = n^7 - n^6.

%F a(n) = A001015(n) - A001014(n).

%F G.f.: 2*(32*x^2 + 473*x^3 + 1208*x^4 + 718*x^5 + 88*x^6 + x^7)/(x - 1)^8. - _Wesley Ivan Hurt_, Aug 03 2014

%F Recurrence: a(n) = 8*a(n-1)-28*a(n-2)+56*a(n-3)-70*a(n-4)+56*a(n-5)-28*(n-6)+8*a(n-7)-a(n-8). - _Wesley Ivan Hurt_, Aug 03 2014

%F Sum_{n>=2} 1/a(n) = 6 - Sum_{k=2..6} zeta(k). - _Amiram Eldar_, Jul 05 2020

%p A240930:=n->n^7-n^6: seq(A240930(n), n=0..30); # _Wesley Ivan Hurt_, Aug 03 2014

%t Table[n^7 - n^6, {n, 0, 30}] (* _Wesley Ivan Hurt_, Aug 03 2014 *)

%t CoefficientList[Series[2 (32*x^2 + 473*x^3 + 1208*x^4 + 718*x^5 + 88*x^6 + x^7)/(x - 1)^8, {x, 0, 30}], x] (* _Wesley Ivan Hurt_, Aug 03 2014 *)

%o (PARI) vector(100, n, (n-1)^7 - (n-1)^6) \\ _Derek Orr_, Aug 03 2014

%o (Magma) [n^7-n^6 : n in [0..30]]; // _Wesley Ivan Hurt_, Aug 03 2014

%Y Cf. A001014, A001015.

%Y Cf. A002378, A045991, A085537, A085538, A085539, A240931, A240932, A240933.

%K nonn,easy

%O 0,3

%A _Martin Renner_, Aug 03 2014