Placid Platypus

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Revision as of 17:02, 28 September 2026 by Sligocki (talk | contribs) (Good point about the Sigma vs S issue, sigh. This also makes it unclear to me if it is computable. I think the S version would be, but not the Sigma version.)
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The Placid Platypus function PP(n) [1] is the minimal number of states of 2-symbol Turing machines that print exactly n ones when halt.

PP(n)≤n, because you can print each 1 in a state. Also if n>Σ(m), then PP(n)>m. On the other side, there is also a connection to a variation of the Lazy Beaver function (determined by ones rather than steps): if n<LBΣ(m) then PP(n)≤m.

Note that this function is not strictly increasing, and that it may be computable.

Values

n PP(n) Example TM
1 1 1RZ--- (bbch)
2 2 1RB---_1RZ--- (bbch)
3 2 1RB1LA_1LA1RZ (bbch)
4 2 1RB1LB_1LA1RZ (bbch)
5 3 1RB1RZ_1LB0RC_1LC1LA (bbch)
6 3 1RB1RZ_0RC1RB_1LC1LA (bbch)
7 4 1RB1LC_0RC0RB_0LD0LA_1LA1RZ (bbch)
8 4 1RB1RZ_1LC0RD_1LA1LB_0LC1RD (bbch)
9 4 1RB1LD_1LC0RB_1RA1LA_1RZ0LC (bbch)
10 4 1RB1RZ_1LC1RA_0RC0LD_1RD0LB (bbch)
11 4 1RB1LD_0LC0RC_1LC1LA_1RZ0LA (bbch)
12 4 1RB0RD_1LC0LA_1RA1LB_1RZ0RC (bbch)
13 4 1RB1LB_1LA0LC_1RZ1LD_1RD0RA (bbch)
14 5 1RB0LB_0LC1RZ_1LE0RD_1RC0RA_1LD0LB (bbch)
15 5 1RB0LD_1LC0LB_1RD0RC_1LA0RE_1RA1RZ (bbch)

References