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 A375020 #21 Aug 05 2024 01:57:07 %S A375020 1,6,970,101130,10129180,1013176996,101320714074,10132113873280, %T A375020 1013211797886962,101321183436796684,10132118360452306248, %U A375020 1013211836390484051818,101321183641942857932324,10132118364229503528908162,1013211836423347845936784704 %N A375020 Alternating sum phi(1) - phi(2) + phi(3) - phi(4) + ... + ((-1)^(10^n+1))*phi(10^n). %C A375020 Digits of terms converge towards 1/Pi^2 = 0.1013211836423... %F A375020 a(n) = A068773(10^n). %o A375020 (Python) %o A375020 # uses code from A002088 and A049690 %o A375020 def A375020(n): return A002088(10**n)-(A049690(10**n>>1)<<1) %Y A375020 Cf. A002088, A049690, A068773. %K A375020 nonn %O A375020 0,2 %A A375020 _Chai Wah Wu_, Aug 04 2024