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 A140730 #24 Jan 19 2023 02:17:26
%S A140730 1,2,3,4,5,10,15,20,25,50,75,100,125,250,375,500,625,1250,1875,2500,
%T A140730 3125,6250,9375,12500,15625,31250,46875,62500,78125,156250,234375,
%U A140730 312500,390625,781250,1171875,1562500,1953125,3906250,5859375,7812500
%N A140730 a(4*n)=5^n, a(4*n+1)=2*5^n, a(4*n+2)=3*5^n, a(4*n+3)=4*5^n.
%H A140730 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,5).
%F A140730 a(n+1) = a(n) + a(n - n mod 4).
%F A140730 a(n) = A140740(n+4,4).
%F A140730 O.g.f.: (1+2*x+3*x^2+4*x^3)/(1-5*x^4). - _R. J. Mathar_, May 31 2008
%F A140730 a(n) = (n+1-4*floor(n/4))*5^floor(n/4). - _Luce ETIENNE_, Aug 05 2015
%F A140730 a(n) = 5*a(n-4) for n>3; a(n) = n+1 for n<5. - _Bruno Berselli_, Aug 05 2015
%F A140730 Sum_{n>=0} 1/a(n) = 125/48. - _Amiram Eldar_, Jan 21 2022
%t A140730 Table[(n + 1 - 4 Floor[n/4]) 5^Floor[n/4], {n, 0, 40}] (* _Bruno Berselli_, Aug 05 2015 *)
%t A140730 LinearRecurrence[{0,0,0,5},{1,2,3,4},40] (* _Harvey P. Dale_, Jul 01 2022 *)
%o A140730 (PARI) a(n)=(n+1-n\4*4)*5^(n\4) \\ _Charles R Greathouse IV_, Oct 07 2015
%o A140730 (Python)
%o A140730 def A140730(n): return ((n&3)+1)*5**(n>>2) # _Chai Wah Wu_, Jan 18 2023
%Y A140730 Cf. A000079, A037124, A038754, A133464, A140740.
%K A140730 nonn,easy
%O A140730 0,2
%A A140730 _Reinhard Zumkeller_, May 26 2008