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%I #128 Jun 05 2022 13:19:25
%S 1,1,2,2,7,9,29,47,144,264,747,1531,4147,9063,23744,54522,140223,
%T 332033,845111,2045007,5176880,12713772,32115727,79676437,201227865,
%U 502852973
%N a(n) is the number of multisets of integers that are possible to reach by starting with n occurrences of 0 and by splitting. Splitting is taking 2 occurrences of the same integer and incrementing one of them by 1 and decrementing the other occurrence by 1.
%C If the limit of a(n+1)/a(n) exists, then it is contained in the closed interval [2,6.75]. See Links for proof. Reverse splitting is defined in A348532.
%H Tejo Vrush, <a href="/A347913/a347913_3.pdf">Limiting ratio for consecutive terms (Upper bound)</a>
%H Tejo Vrush, <a href="/A347913/a347913_8.pdf">Limiting ratio for consecutive terms (Lower bound)</a>
%e For n = 5, the multisets are as follows:
%e {{0,0,0,0,0}} {{-1,0,0,0,1}} {{-1,-1,0,1,1}}
%e {{-1,-1,0,0,2}} {{-1,-1,-1,1,2}} {{-2,0,0,1,1}}
%e {{-2,0,0,0,2}} {{-2,-1,1,1,1}} {{-2,-1,0,1,2}}
%e Therefore, a(5) = 9.
%e For n = 6, the multisets are as follows:
%e {{0,0,0,0,0,0}} {{-1,0,0,0,0,1}} {{-1,-1,0,0,1,1}}
%e {{-1,-1,0,0,0,2}} {{-1,-1,-1,1,1,1}} {{-1,-1,-1,0,1,2}}
%e {{-2,0,0,0,1,1}} {{-2,0,0,0,0,2}} {{-2,-1,0,1,1,1}}
%e {{-2,-1,0,0,1,2}} {{-2,-1,-1,1,1,2}} {{-2,-1,-1,0,2,2}}
%e {{-2,-1,-1,0,1,3}} {{-2,-2,0,1,1,2}} {{-2,-2,0,0,2,2}}
%e {{-2,-2,0,0,1,3}} {{-2,-2,-1,1,2,2}} {{-2,-2,-1,1,1,3}}
%e {{-2,-2,-1,0,2,3}} {{-3,-1,0,1,1,2}} {{-3,-1,0,0,2,2}}
%e {{-3,-1,0,0,1,3}} {{-3,-1,-1,1,2,2}} {{-3,-1,-1,1,1,3}}
%e {{-3,-1,-1,0,2,3}} {{-3,-2,0,1,2,2}} {{-3,-2,0,1,1,3}}
%e {{-3,-2,0,0,2,3}} {{-3,-2,-1,1,2,3}}
%e Therefore, a(6) = 29.
%p b:= proc(p) option remember; {p, seq(`if`(coeff(p, x, i)>1,
%p b(expand((p-2*x^i+x^(i-1)+x^(i+1))*`if`(i=0, x, 1)
%p )), [])[], i=0..degree(p))}
%p end:
%p a:= n-> nops(b(n)):
%p seq(a(n), n=0..10); # _Alois P. Heinz_, Oct 07 2021
%t b[p_] := b[p] = Union@Flatten@Join[{p}, Table[If[Coefficient[p, x, i] > 1, b[Expand[(p - 2*x^i + x^(i - 1) + x^(i + 1))*If[i == 0, x, 1]]]], {i, 0, Exponent[p, x]}]];
%t a[n_] := If[n == 0, 1, Length[b[n]] - 1];
%t Table[Print[n, " ", a[n]]; a[n], {n, 0, 14}] (* _Jean-François Alcover_, Jun 04 2022, after _Alois P. Heinz_ *)
%o (Python)
%o def nextq(q):
%o used = set()
%o for i in range(len(q)-1):
%o for j in range(i+1, len(q)):
%o if q[i] == q[j]:
%o if q[i] in used: continue
%o used.add(q[i])
%o qc = list(q); qc[i] -= 1; qc[j] += 1
%o yield tuple(sorted(qc))
%o def a(n):
%o s = tuple(0 for i in range(n)); reach = {s}; expand = list(reach)
%o while len(expand) > 0:
%o q = expand.pop()
%o for qq in nextq(q):
%o if qq not in reach:
%o reach.add(qq)
%o if len(set(qq)) < len(qq):
%o expand.append(qq)
%o return len(reach)
%o print([a(n) for n in range(17)]) # _Michael S. Branicky_, Oct 10 2021
%Y Cf. A348532.
%K nonn,more
%O 0,3
%A _Tejo Vrush_, Oct 07 2021
%E a(15)-a(22) from _David A. Corneth_, Oct 08 2021
%E a(23)-a(25) from _Michael S. Branicky_, Oct 12 2021
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