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A036047
Product of order of cycles of the permutation created by duality and reversal on the partitions of n.
1
1, 1, 1, 1, 1, 4, 12, 16, 392, 34, 48, 3244032, 12060, 27540, 6272, 501696, 846000, 119448, 4067265600, 422072987719680, 4338692557056, 28944689875920, 1247499918000000, 43692593457240000, 118467674601420800, 422997472353189888000, 56671603019312949732556800000
OFFSET
1,6
PROG
(PARI)
Dual(v)={my(u=vectorsmall(v[1]), k=0); forstep(i=#u, 1, -1, while(k<#v&&v[k+1]>=i, k++); u[i]=k); u}
OrderCycs(v)={my(t=vector(#v), L=List()); for(i=1, #v, my(c=0, j=i); while(!t[j], t[j]=1; j=v[j]; c++); if(c, listput(L, c))); Vec(L)}
a(n)={my(u=vecsort([Vecsmall(Vecrev(p)) | p<-partitions(n)])); my(v=vector(#u, i, vecsearch(u, Dual(u[#u+1-i])))); vecprod(OrderCycs(v))} \\ Andrew Howroyd, Sep 16 2019
CROSSREFS
KEYWORD
nonn
EXTENSIONS
a(26)-a(27) from Andrew Howroyd, Sep 16 2019
STATUS
approved