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A111588
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Crazy Dice: number of ways to design a pair of n-sided dice with positive integers on their faces, so that the sums when they are tossed occur with the same probabilities as if a pair of standard n-sided dice were tossed.
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3
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1, 1, 1, 2, 1, 2, 1, 4, 2, 2, 1, 8, 1, 2, 2, 10, 1, 8, 1, 8, 2, 2, 1, 33, 2, 2, 4, 8, 1, 13, 1, 26, 2, 2, 2, 57, 1, 2, 2, 33, 1, 13, 1, 8, 8, 2, 1, 140, 2, 8, 2, 8, 1, 33, 2, 33, 2, 2, 1, 125, 1, 2, 8, 71, 2, 13, 1, 8, 2, 13, 1, 348, 1, 2, 8, 8, 2, 13, 1, 140, 10, 2, 1, 122, 2, 2, 2, 33, 1, 118, 2
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OFFSET
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1,4
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COMMENTS
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It is not required that the two dice be identical, it is not required that the entries be bounded by n and we do not ask that the entries be distinct from one another on each cube.
We pretend for the purpose of this sequence that regular n-sided dice exist for all n.
In other words, how many (unordered) pairs of polynomials B(x) = x^b_1 + x^b_2 + ... + x^b_n, C(x) = x^c_1 + x^c_2 + ... + x^c_n, are there with all exponents positive integers, such that B(x)*C(x) = (x+x^2+x^3+...+x^n)^2?
a(n) = 1 means that the only way two n-sided dice can have the same probability distribution as two normal n-sided dice (each side numbered 1 through n) is if they are normal. a(6) = 2 corresponds to normal dice and Sicherman dice (one labeled 1,2,2,3,3,4 and the other 1,3,4,5,6,8). - Charles R Greathouse IV, Jan 19 2017
Records are: 1, 2, 4, 8, 10, 33, 57, 140, 348, 583, 956, 2036, 2393, 3050, ... and they seem to occur at positions given by A033833. - Antti Karttunen, Aug 28 2017
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REFERENCES
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M. Gardner, "Penrose Tiles to Trapdoor Ciphers", p. 266.
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LINKS
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EXAMPLE
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The first nontrivial example is for n=4: {1,2,2,3} and {1,3,3,5} together have the same sum probabilities as a pair of {1,2,3,4}. That is, (x + 2x^2 + x^3)(x + 2x^3 + x^5)=(x + x^2 + x^3 + x^4)^2.
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PROG
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(PARI) ok(p, e, n)=my(v=Vec(factorback(p, e))); vecmin(v)>=0 && vecsum(v)==n
a(n)=if(n<4, return(1)); my(x='x, f=factor((x^n-1)/(x-1)), p=f[, 1], e=2*f[, 2]~, u=vector(#e, i, [0, e[i]]), s, t); t=vecmax(e); for(i=1, #e, if(e[i]==t, u[i][2]\=2; break)); forvec(v=u, t=e-v; if(cmp(v, t)<=0 && ok(p, v, n) && ok(p, t, n), s++)); s \\ Charles R Greathouse IV, Jan 19 2017
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Correction to some terms, thanks to Adam Chalcraft. - Matthew Conroy, Apr 04 2010
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STATUS
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approved
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