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 A141426 #12 Jul 22 2025 13:12:11
%S A141426 1,2,18,28,42,58,70,78,88,108,112,126,136,138,148,162,178,180,196,198,
%T A141426 210,228,238,240,268,280,282,292,312,316,336,348,358,378,388,396,400,
%U A141426 408,418,420,430,438,448,462,466,478,486,490,498,508,520,522,546,568
%N A141426 a(n) = A140555(n) - 1.
%C A141426 Previous name was: Count of numbers smaller than and coprime to the prime A140555(n).
%F A141426 a(n) = phi(A140555(n)) = A140555(n) - 1.
%p A141426 isA140555 := proc(n) RETURN( isprime(n) and not isprime(n+6) ) ; end: A140555 := proc(n) option remember ; if n = 1 then 2; else for a from procname(n-1)+1 do if isA140555(a) then RETURN(a) ; fi; od: fi; end: A141426 := proc(n) A140555(n)-1 ; end: for n from 1 to 100 do printf("%d,",A141426(n)) ; od: # _R. J. Mathar_, Aug 12 2008
%t A141426 lim=255;a140555=Select[Prime[Range[lim]], !PrimeQ[#+6]&];a[n_]:=Total[Boole[CoprimeQ[Range[a141426[[n]]-1],a140555[[n]]]]];Array[a,PrimePi[lim]] (* _James C. McMahon_, Jul 22 2025 *)
%Y A141426 Cf. A140555.
%K A141426 nonn,less
%O A141426 1,2
%A A141426 _Giovanni Teofilatto_, Aug 06 2008
%E A141426 Edited and extended by _R. J. Mathar_, Aug 12 2008
%E A141426 New name from _Joerg Arndt_, Jul 22 2025