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.
a(8) = 3 because 1, 5 and 7 are all relatively prime to both 8 and 9. a(9) counts those numbers coprime to 90, i.e., 1 and 7, hence a(9) = 2.
[#[k:k in [1..n]| Gcd(n,k) eq Gcd(n+1,k) and Gcd(n,k) eq 1]: n in [1..80]]; // Marius A. Burtea, Oct 15 2019
A057475 := proc(n) local a,k ; a := 0; for k from 1 to n do if igcd(k,n) = 1 and igcd(k,n+1)=1 then a := a+1 ; end if; end do: a ; end proc: seq(A057475(n),n=1..80) ; # R. J. Mathar, May 13 2025
a[ n_ ] := Length @ Select[ Range[ n ], GCD[ n, # ] == GCD[ n + 1, # ] == 1 & ]; Table[ a[ n ], {n, 80} ] (* Ray Chandler, Dec 06 2006 *)
newphi(v)=local(vl,fl,np); vl=length(v); np=0; for (s=1,v[1],fl=false; for (r=1,vl,if (gcd(s,v[r])>1,fl=true; break)); if (fl==false,np++)); np v=vector(2); for (i=1,500,v[1]=i; v[2]=i+1; print1(newphi(v)","))
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