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A061417 Number of permutations up to cyclic rotations; permutation siteswap necklaces. 11
1, 2, 4, 10, 28, 136, 726, 5100, 40362, 363288, 3628810, 39921044, 479001612, 6227066928, 87178295296, 1307675013928, 20922789888016, 355687438476444, 6402373705728018, 121645100594641896, 2432902008177690360 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

If permutations are converted to (i,p(i)) permutation arrays, then this automorphism is obtained by their "SW-NE 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 Egri-Nagy, Aug 15 2014

LINKS

T. D. Noe, Table of n, a(n) for n=1..100

Index entries for sequences related to necklaces

FORMULA

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

EXAMPLE

If I have a five-element permutation like 25431, in cycle notation (1 2 5)(3 4), I mark the numbers 1-5 clockwise onto a circle and draw directed edges from 1 to 2, from 2 to 5, from 5 to 1 and a double-way edge between 3 and 4. All the 5-element 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 u-1 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/((n-1)!)); RETURN(PermUnrank3Rfixaux(n-1, r-(s*((n-1)!)), permul(p, [[n, n-s]]))); 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}] (* Jean-Fran├žois Alcover, Oct 09 2012, from formula *)

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 Egri-Nagy, 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 xrange(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] = (p-1)!+(p-1) for all prime p's.

A064636 (derangements-the same automorphism).

A061417[n] = A064649[n]/n.

Sequence in context: A207018 A006841 A003223 * A153921 A189582 A060315

Adjacent sequences:  A061414 A061415 A061416 * A061418 A061419 A061420

KEYWORD

nonn,easy,nice

AUTHOR

Antti Karttunen, May 02 2001

STATUS

approved

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Last modified December 12 20:04 EST 2017. Contains 295954 sequences.