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.
%I A059897 #48 Feb 16 2025 08:32:44
%S A059897 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,
%T A059897 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,
%U A059897 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
%N 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.
%C A059897 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.
%C A059897 Analogous to multiplication, with XOR replacing +.
%C A059897 From _Peter Munn_, Apr 01 2019: (Start)
%C A059897 (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.
%C A059897 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).
%C A059897 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.
%C A059897 It is a subgroup of the equivalent group over the nonzero integers, which has -1 as an additional generator.
%C A059897 As generated by A050376, the subgroup of even length words is A000379. The complementary set of odd length words is A000028.
%C A059897 The subgroup generated by A000040 (the primes) is A005117 (the squarefree numbers).
%C A059897 (End)
%C A059897 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
%H A059897 Antti Karttunen, <a href="/A059897/b059897.txt">Table of n, a(n) for n = 1..10440; the first 144 antidiagonals of the array</a>
%H A059897 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Group.html">Group</a>, <a href="https://mathworld.wolfram.com/SquarePart.html">Square Part</a>, <a href="https://mathworld.wolfram.com/SquarefreePart.html">Squarefree Part</a>.
%F A059897 For all x, y >= 1, A(x,y) * A059895(x,y)^2 = x*y. - _Antti Karttunen_, Apr 11 2017
%F A059897 From _Peter Munn_, Apr 01 2019: (Start)
%F A059897 A(n,1) = A(1,n) = n
%F A059897 A(n, A(m,k)) = A(A(n,m), k)
%F A059897 A(n,n) = 1
%F A059897 A(n,k) = A(k,n)
%F A059897 if i_1 <> i_2 then A(A050376(i_1), A050376(i_2)) = A050376(i_1) * A050376(i_2)
%F A059897 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)
%F A059897 (End)
%F A059897 T(k, m) = k*m for coprime k and m. - _David A. Corneth_, Apr 03 2019
%F A059897 if A(n*m,m) = n, A(n*m,k) = A(n,k) * A(m,k) / k. - _Peter Munn_, Apr 04 2019
%F A059897 A(n,k) = A007913(n*k) * A(A000188(n), A000188(k))^2. - _Peter Munn_, Mar 21 2022
%e A059897 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.
%e A059897 The top left 12 X 12 corner of the array:
%e A059897 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
%e A059897 2, 1, 6, 8, 10, 3, 14, 4, 18, 5, 22, 24
%e A059897 3, 6, 1, 12, 15, 2, 21, 24, 27, 30, 33, 4
%e A059897 4, 8, 12, 1, 20, 24, 28, 2, 36, 40, 44, 3
%e A059897 5, 10, 15, 20, 1, 30, 35, 40, 45, 2, 55, 60
%e A059897 6, 3, 2, 24, 30, 1, 42, 12, 54, 15, 66, 8
%e A059897 7, 14, 21, 28, 35, 42, 1, 56, 63, 70, 77, 84
%e A059897 8, 4, 24, 2, 40, 12, 56, 1, 72, 20, 88, 6
%e A059897 9, 18, 27, 36, 45, 54, 63, 72, 1, 90, 99, 108
%e A059897 10, 5, 30, 40, 2, 15, 70, 20, 90, 1, 110, 120
%e A059897 11, 22, 33, 44, 55, 66, 77, 88, 99, 110, 1, 132
%e A059897 12, 24, 4, 3, 60, 8, 84, 6, 108, 120, 132, 1
%e A059897 From _Peter Munn_, Apr 04 2019: (Start)
%e A059897 The subgroup generated by {6,8,10}, the first three integers > 1 not in A050376, has the following table:
%e A059897 1 6 8 10 12 15 20 120
%e A059897 6 1 12 15 8 10 120 20
%e A059897 8 12 1 20 6 120 10 15
%e A059897 10 15 20 1 120 6 8 12
%e A059897 12 8 6 120 1 20 15 10
%e A059897 15 10 120 6 20 1 12 8
%e A059897 20 120 10 8 15 12 1 6
%e A059897 120 20 15 12 10 8 6 1
%e A059897 (End)
%t A059897 a[i_, i_] = 1;
%t A059897 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]]])];
%t A059897 Table[a[i - j + 1, j], {i, 1, 15}, {j, 1, i}] // Flatten (* _Jean-François Alcover_, Jun 19 2018 *)
%o A059897 (Scheme)
%o A059897 (define (A059897 n) (A059897bi (A002260 n) (A004736 n)))
%o A059897 (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)))))))
%o A059897 ;; _Antti Karttunen_, Apr 11 2017
%o A059897 (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
%o A059897 (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
%o A059897 (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
%Y A059897 Cf. A000040, A003987, A003991, A028233, A028234, A050376, A059896, A089913, A207901, A268387, A284577, A302033.
%Y A059897 Cf. A284567 (A000142 or A003418-analog for this operation).
%Y A059897 Rows/columns: A073675 (2), A120229 (3), A120230 (4), A307151 (5), A307150 (6), A307266 (8), A307267 (24).
%Y A059897 Particularly significant subgroups or cosets: A000028, A000379, A003159, A005117, A030229, A252895. See also the lists in A329050, A352273.
%Y A059897 Sequences that relate this sequence to multiplication: A000188, A007913, A059895.
%K A059897 base,easy,nonn,tabl,nice,look
%O A059897 1,2
%A A059897 _Marc LeBrun_, Feb 06 2001
%E A059897 New name from _Peter Munn_, Mar 21 2022