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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 Fermi-Dirac 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 (list; table; graph; refs; listen; history; text; internal format)
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 +.
From Peter Munn, Apr 01 2019: (Start)
(1) Defines an abelian group whose underlying set is the positive integers. (2) Every element is self-inverse. (3) For all n and k, A(n,k) is a divisor of n*k. (4) The terms of A050376, sometimes called Fermi-Dirac 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 self-inverse 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
Eric Weisstein's World of Mathematics, Group, Square Part, Squarefree Part.
FORMULA
For all x, y >= 1, A(x,y) * A059895(x,y)^2 = x*y. - Antti Karttunen, Apr 11 2017
From Peter Munn, Apr 01 2019: (Start)
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 i_1 <> i_2 then A(A050376(i_1), A050376(i_2)) = A050376(i_1) * A050376(i_2)
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)
T(k, m) = k*m for coprime k and m. - David A. Corneth, Apr 03 2019
if A(n*m,m) = n, A(n*m,k) = A(n,k) * A(m,k) / k. - Peter Munn, Apr 04 2019
A(n,k) = A007913(n*k) * A(A000188(n), A000188(k))^2. - Peter Munn, Mar 21 2022
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
From Peter Munn, Apr 04 2019: (Start)
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]]])];
Table[a[i - j + 1, j], {i, 1, 15}, {j, 1, i}] // Flatten (* Jean-François Alcover, Jun 19 2018 *)
PROG
(Scheme)
(define (A059897 n) (A059897bi (A002260 n) (A004736 n)))
(define (A059897bi a b) (let loop ((a a) (b b) (m 1)) (cond ((= 1 a) (* m b)) ((= 1 b) (* m a)) ((equal? (A020639 a) (A020639 b)) (loop (A028234 a) (A028234 b) (* m (expt (A020639 a) (A003987bi (A067029 a) (A067029 b)))))) ((< (A020639 a) (A020639 b)) (loop (/ a (A028233 a)) b (* m (A028233 a)))) (else (loop a (/ b (A028233 b)) (* m (A028233 b)))))))
;; Antti Karttunen, Apr 11 2017
(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
(PARI) A059897(n, k) = if(n==k, 1, core(n*k) * A059897(core(n, 1)[2], core(k, 1)[2])^2) \\ Peter Munn, Mar 21 2022
CROSSREFS
Cf. A284567 (A000142 or A003418-analog for this operation).
Rows/columns: A073675 (2), A120229 (3), A120230 (4), A307151 (5), A307150 (6), A307266 (8), A307267 (24).
Particularly significant subgroups or cosets: A000028, A000379, A003159, A005117, A030229, A252895. See also the lists in A329050, A352273.
Sequences that relate this sequence to multiplication: A000188, A007913, A059895.
Sequence in context: A341458 A089913 A257522 * A325821 A341607 A303719
KEYWORD
base,easy,nonn,tabl,nice,look
AUTHOR
Marc LeBrun, Feb 06 2001
EXTENSIONS
New name from Peter Munn, Mar 21 2022
STATUS
approved

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Last modified February 28 22:27 EST 2024. Contains 370400 sequences. (Running on oeis4.)