OFFSET
1,5
REFERENCES
M. Lal, H. Wareham and R. Mifflin, Iterates of the bi-unitary totient function, Utilitas Math., 10 (1976), 347-350.
LINKS
FORMULA
T(m,n) = T(n,m) = A165430(n,m).
EXAMPLE
Array begins
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, ...
1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, ...
1, 1, 3, 1, 1, 3, 1, 1, 1, 1, 1, 3, ...
1, 1, 1, 4, 1, 1, 1, 1, 1, 1, 1, 4, ...
1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, ...
1, 2, 3, 1, 1, 6, 1, 1, 1, 2, 1, 3, ...
1, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, ...
1, 1, 1, 1, 1, 1, 1, 8, 1, 1, 1, 1, ...
...
The unitary divisors of 3 are 1 and 3, those of 6 are 1,2,3,6; so T(6,3) = T(3,6) = 3.
MAPLE
# returns the greatest common unitary divisor of m and n
f:=proc(m, n)
local i, ans;
ans:=1;
for i from 1 to min(m, n) do
if ((m mod i) = 0) and (igcd(i, m/i) = 1) then
if ((n mod i) = 0) and (igcd(i, n/i) = 1) then ans:=i; fi;
fi;
od;
ans; end;
MATHEMATICA
f[m_, n_] := Module[{i, ans=1}, For[i=1, i<=Min[m, n], i++, If[Mod[m, i]==0 && GCD[i, m/i]==1, If[Mod[n, i]==0 && GCD[i, n/i]==1, ans=i]]]; ans];
Table[f[m-n+1, n], {m, 1, 14}, {n, 1, m}] // Flatten (* Jean-François Alcover, Jun 19 2018, translated from Maple *)
PROG
(PARI)
up_to = 20100; \\ = binomial(200+1, 2)
A225174sq(m, n) = { my(a=min(m, n), b=max(m, n), md=0); fordiv(a, d, if(0==(b%d)&&1==gcd(d, a/d)&&1==gcd(d, b/d), md=d)); (md); };
A225174list(up_to) = { my(v = vector(up_to), i=0); for(a=1, oo, for(col=1, a, if(i++ > up_to, return(v)); v[i] = A225174sq((a-(col-1)), col))); (v); };
v225174 = A225174list(up_to);
A225174(n) = v225174[n]; \\ Antti Karttunen, Nov 28 2018
CROSSREFS
AUTHOR
N. J. A. Sloane, May 01 2013
STATUS
approved