

A059897


Symmetric square array read by antidiagonals: A(n,k) is the product of all factors that occur in one, but not both, of the FermiDirac factorizations of n and k.


80



1, 2, 2, 3, 1, 3, 4, 6, 6, 4, 5, 8, 1, 8, 5, 6, 10, 12, 12, 10, 6, 7, 3, 15, 1, 15, 3, 7, 8, 14, 2, 20, 20, 2, 14, 8, 9, 4, 21, 24, 1, 24, 21, 4, 9, 10, 18, 24, 28, 30, 30, 28, 24, 18, 10, 11, 5, 27, 2, 35, 1, 35, 2, 27, 5, 11, 12, 22, 30, 36, 40, 42, 42, 40, 36, 30, 22, 12, 13, 24, 33
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OFFSET

1,2


COMMENTS

Old name: Square array read by antidiagonals: T(i,j) = product prime(k)^(Ei(k) XOR Ej(k)) where Ei and Ej are the vectors of exponents in the prime factorizations of i and j; XOR is the bitwise operation on binary representation of the exponents.
Analogous to multiplication, with XOR replacing +.
(1) Defines an abelian group whose underlying set is the positive integers. (2) Every element is selfinverse. (3) For all n and k, A(n,k) is a divisor of n*k. (4) The terms of A050376, sometimes called FermiDirac primes, form a minimal set of generators. In ordered form, it is the lexicographically earliest such set.
The unique factorization of positive integers into products of distinct terms of the group's lexicographically earliest minimal set of generators seems to follow from (1) (2) and (3).
From (1) and (2), every row and every column of the table is a selfinverse permutation of the positive integers. Rows/columns numbered by nonmembers of A050376 are compositions of earlier rows/columns.
It is a subgroup of the equivalent group over the nonzero integers, which has 1 as an additional generator.
As generated by A050376, the subgroup of even length words is A000379. The complementary set of odd length words is A000028.
The subgroup generated by A000040 (the primes) is A005117 (the squarefree numbers).
(End)
Considered as a binary operation, the result is (the squarefree part of the product of its operands) times the square of (the operation's result when applied to the square roots of the square parts of its operands).  Peter Munn, Mar 21 2022


LINKS



FORMULA

A(n,1) = A(1,n) = n
A(n, A(m,k)) = A(A(n,m), k)
A(n,n) = 1
A(n,k) = A(k,n)
if A(n,k_1) = n * k_1 and A(n,k_2) = n * k_2 then A(n, A(k_1,k_2)) = n * A(k_1,k_2)
(End)
if A(n*m,m) = n, A(n*m,k) = A(n,k) * A(m,k) / k.  Peter Munn, Apr 04 2019


EXAMPLE

A(864,1944) = A(2^5*3^3,2^3*3^5) = 2^(5 XOR 3) * 3^(3 XOR 5) = 2^6 * 3^6 = 46656.
The top left 12 X 12 corner of the array:
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
2, 1, 6, 8, 10, 3, 14, 4, 18, 5, 22, 24
3, 6, 1, 12, 15, 2, 21, 24, 27, 30, 33, 4
4, 8, 12, 1, 20, 24, 28, 2, 36, 40, 44, 3
5, 10, 15, 20, 1, 30, 35, 40, 45, 2, 55, 60
6, 3, 2, 24, 30, 1, 42, 12, 54, 15, 66, 8
7, 14, 21, 28, 35, 42, 1, 56, 63, 70, 77, 84
8, 4, 24, 2, 40, 12, 56, 1, 72, 20, 88, 6
9, 18, 27, 36, 45, 54, 63, 72, 1, 90, 99, 108
10, 5, 30, 40, 2, 15, 70, 20, 90, 1, 110, 120
11, 22, 33, 44, 55, 66, 77, 88, 99, 110, 1, 132
12, 24, 4, 3, 60, 8, 84, 6, 108, 120, 132, 1
The subgroup generated by {6,8,10}, the first three integers > 1 not in A050376, has the following table:
1 6 8 10 12 15 20 120
6 1 12 15 8 10 120 20
8 12 1 20 6 120 10 15
10 15 20 1 120 6 8 12
12 8 6 120 1 20 15 10
15 10 120 6 20 1 12 8
20 120 10 8 15 12 1 6
120 20 15 12 10 8 6 1
(End)


MATHEMATICA

a[i_, i_] = 1;
a[i_, j_] := Module[{f1 = FactorInteger[i], f2 = FactorInteger[j], e1, e2}, e1[_] = 0; Scan[(e1[#[[1]]] = #[[2]])&, f1]; e2[_] = 0; Scan[(e2[#[[1]]] = #[[2]])&, f2]; Times @@ (#^BitXor[e1[#], e2[#]]& /@ Union[f1[[All, 1]], f2[[All, 1]]])];


PROG

(Scheme)
(PARI) T(n, k) = {if (n==1, return (k)); if (k==1, return (n)); my(fn=factor(n), fk=factor(k)); vp = setunion(fn[, 1]~, fk[, 1]~); prod(i=1, #vp, vp[i]^(bitxor(valuation(n, vp[i]), valuation(k, vp[i])))); } \\ Michel Marcus, Apr 03 2019
(PARI) T(i, j) = {if(gcd(i, j) == 1, return(i * j)); if(i == j, return(1)); my(f = vecsort(concat(factor(i)~, factor(j)~)), t = 1, res = 1); while(t + 1 <= #f, if(f[1, t] == f[1, t+1], res *= f[1, t] ^ bitxor(f[2, t] , f[2, t+1]); t+=2; , res*= f[1, t]^f[2, t]; t++; ) ); if(t == #f, res *= f[1, #f] ^ f[2, #f]); res } \\ David A. Corneth, Apr 03 2019


CROSSREFS

Cf. A000040, A003987, A003991, A028233, A028234, A050376, A059896, A089913, A207901, A268387, A284577, A302033.


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STATUS

approved



