This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A050989 #39 Feb 16 2025 08:32:41
%S A050989 1,56,1764,41160,792330,13311144,201885684,2826399576,37096494435,
%T A050989 461645264080,5493578642552,62926446269232,697434779483988,
%U A050989 7510836086750640,78863778910881720,809668130151718992,8147285559651672357,80514351413028291528,782778416515552834300
%N A050989 7-idempotent numbers.
%H A050989 Vincenzo Librandi, <a href="/A050989/b050989.txt">Table of n, a(n) for n = 7..400</a>
%H A050989 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/IdempotentNumber.html">Idempotent Number</a>.
%H A050989 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (56,-1372,19208,-168070,941192,-3294172,6588344,-5764801).
%F A050989 a(n) = C(n, 7)*7^(n-7).
%F A050989 G.f.: x^7/(1-7*x)^8.
%F A050989 From _Amiram Eldar_, Apr 17 2022: (Start)
%F A050989 Sum_{n>=7} 1/a(n) = 2286144*log(7/6) - 10572289/30.
%F A050989 Sum_{n>=7} (-1)^(n+1)/a(n) = 12845056*log(8/7) - 51456517/30. (End)
%p A050989 seq(binomial(n, 7)*7^(n-7), n=7..33); # _Zerinvary Lajos_, Aug 01 2008
%t A050989 LinearRecurrence[{56,-1372,19208,-168070,941192,-3294172,6588344,-5764801}, {1,56,1764,41160,792330,13311144,201885684,2826399576},20] (* _Harvey P. Dale_, May 31 2014 *)
%o A050989 (PARI) a(n)=binomial(n, 7)*7^(n-7) \\ _Charles R Greathouse IV_, Sep 03 2011
%o A050989 (Magma) [7^(n-7)* Binomial(n, 7): n in [7..30]]; // _Vincenzo Librandi_, Oct 16 2011
%Y A050989 Cf. A001788, A036216, A040075, A050982, A050988, A059297, A059300.
%K A050989 nonn,easy
%O A050989 7,2
%A A050989 _Eric W. Weisstein_