

A061417


Number of permutations up to cyclic rotations; permutation siteswap necklaces.


16



1, 2, 4, 10, 28, 136, 726, 5100, 40362, 363288, 3628810, 39921044, 479001612, 6227066928, 87178295296, 1307675013928, 20922789888016, 355687438476444, 6402373705728018, 121645100594641896, 2432902008177690360
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OFFSET

1,2


COMMENTS

If permutations are converted to (i,p(i)) permutation arrays, then this automorphism is obtained by their "SWNE diagonal toroidal shifts" (see Matthias Engelhardt's Java program in A006841), while the Maple procedure below converts each permutation to a siteswap pattern (used in juggling), rotates it by one digit and converts the resulting new (or same) siteswap pattern back to a permutation.
When the subset of permutations listed by A064640 are subjected to the same automorphism one gets A002995.
The number of conjugacy classes of the symmetric group of degree n when conjugating only with the cyclic permutation group of degree n.  Attila EgriNagy, Aug 15 2014
Also the number of equivalence classes of permutations of {1...n} under the action of rotation of vertices in the cycle decomposition. The corresponding action on words applies m > m + 1 for m < n and n > 1, and rotates once to the right. For example, (24531) first becomes (35142) under the application of cyclic rotation, and then is rotated right to give (23514).  Gus Wiseman, Mar 04 2019


LINKS

T. D. Noe, Table of n, a(n) for n=1..100
Index entries for sequences related to necklaces
Gus Wiseman, Inequivalent representatives of the a(5) = 28 permutations under rotation of vertices in the cycle decomposition.


FORMULA

a(n) = (1/n)*Sum_{dn} phi(n/d)*((n/d)^d)*(d!).


EXAMPLE

If I have a fiveelement permutation like 25431, in cycle notation (1 2 5)(3 4), I mark the numbers 15 clockwise onto a circle and draw directed edges from 1 to 2, from 2 to 5, from 5 to 1 and a doubleway edge between 3 and 4. All the 5element permutations that produce some rotation (discarding the labels of the nodes) of that chord diagram belong to the same equivalence class with 25431. The sequence gives the count of such equivalence classes.


MAPLE

Algebraic formula: with(numtheory); SSRPCC := proc(n) local d, s; s := 0; for d in divisors(n) do s := s + phi(n/d)*((n/d)^d)*(d!); od; RETURN(s/n); end;
Empirically: with(group); SiteSwapRotationPermutationCycleCounts := proc(upto_n) local b, u, n, a, r; a := []; for n from 1 to upto_n do b := []; u := n!; for r from 0 to u1 do b := [op(b), 1+PermRank3R(SiteSwap2Perm1(rotateL(Perm2SiteSwap2(PermUnrank3Rfix(n, r)))))]; od; a := [op(a), CountCycles(b)]; od; RETURN(a); end;
PermUnrank3Rfixaux := proc(n, r, p) local s; if(0 = n) then RETURN(p); else s := floor(r/((n1)!)); RETURN(PermUnrank3Rfixaux(n1, r(s*((n1)!)), permul(p, [[n, ns]]))); fi; end;
PermUnrank3Rfix := (n, r) > convert(PermUnrank3Rfixaux(n, r, []), 'permlist', n);
SiteSwap2Perm1 := proc(s) local e, n, i, a; n := nops(s); a := []; for i from 1 to n do e := ((i+s[i]) mod n); if(0 = e) then e := n; fi; a := [op(a), e]; od; RETURN(convert(invperm(convert(a, 'disjcyc')), 'permlist', n)); end;


MATHEMATICA

a[n_] := (1/n)*Sum[ EulerPhi[n/d]*(n/d)^d*d!, {d, Divisors[n]}]; Table[a[n], {n, 1, 21}] (* JeanFrançois Alcover, Oct 09 2012, from formula *)
Table[Length[Select[Permutations[Range[n]], #==First[Sort[NestList[RotateRight[#/.k_Integer:>If[k==n, 1, k+1]]&, #, n1]]]&]], {n, 8}] (* Gus Wiseman, Mar 04 2019 *)


PROG

(Haskell)
a061417 = sum . a047917_row  Reinhard Zumkeller, Mar 19 2014
(GAP) List([1..10], n>Size( OrbitsDomain( CyclicGroup(I sPermGroup, n), SymmetricGroup( IsPermGroup, n), \^))); # Attila EgriNagy, Aug 15 2014
(PARI) a(n) = (1/n)*sumdiv(n, d, eulerphi(n/d)*(n/d)^d*d!); \\ Indranil Ghosh, Apr 10 2017
(Python)
from sympy import divisors, factorial, totient
def a(n): return sum([totient(n/d)*(n/d)**d*factorial(d) for d in divisors(n)])/n
print [a(n) for n in range(1, 22)] # Indranil Ghosh, Apr 10 2017


CROSSREFS

Cf. A006841, A060495. For other Maple procedures, see A060501 (Perm2SiteSwap2), A057502 (CountCycles), A057509 (rotateL), A060125 (PermRank3R and permul).
A061417[p] = A061860[p] = (p1)!+(p1) for all prime p's.
A064636 (derangementsthe same automorphism).
A061417[n] = A064649[n]/n.
Cf. A000031, A000939, A008965, A060223, A086675 (digraphical necklaces), A179043, A192332, A275527 (path necklaces), A323858, A323859, A323870, A324513, A324514 (aperiodic permutations).
Sequence in context: A207018 A006841 A003223 * A153921 A189582 A060315
Adjacent sequences: A061414 A061415 A061416 * A061418 A061419 A061420


KEYWORD

nonn,easy,nice,changed


AUTHOR

Antti Karttunen, May 02 2001


STATUS

approved



