OFFSET
1,8
FORMULA
Sum_{k=1..n, gcd(n,k)=1} a(k) = 1 when n=4, 0 elsewhere.
MATHEMATICA
M[n_] := M[n] = Inverse[Table[If[r >= c, If[GCD[r-c+1, c] == 1, 1, 0], 0], {r, 1, n}, {c, 1, n}]];
T[n_, k_] := If[n<k || k<0, 0, M[n][[n, k]]];
a[n_] := T[n, 3];
Array[a, 90] (* Jean-François Alcover, Oct 27 2018, from PARI *)
PROG
(PARI) {a(n)=(matrix(n+2, n+2, r, c, if(r>=c, if(gcd(r-c+1, c)==1, 1, 0)))^-1)[n, 3]}
CROSSREFS
KEYWORD
sign
AUTHOR
Leroy Quet, Paul D. Hanna, Apr 16 2006
STATUS
approved