cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A330935 Irregular triangle read by rows where T(n,k) is the number of length-k chains from minimum to maximum in the poset of factorizations of n into factors > 1, ordered by refinement.

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%I A330935 #6 Jan 05 2020 08:11:12
%S A330935 1,1,0,1,1,0,1,1,0,1,1,0,1,0,1,1,0,1,2,1,0,1,0,1,0,1,3,2,1,0,1,2,1,0,
%T A330935 1,2,0,1,0,1,1,0,1,5,5,0,1,0,1,0,1,1,0,1,2,1,0,1,3,1,0,1,5,8,4,0,1,0,
%U A330935 1,0,1,0,1,7,7,1,0,1,0,1,0,1,5,5,1,0,1
%N A330935 Irregular triangle read by rows where T(n,k) is the number of length-k chains from minimum to maximum in the poset of factorizations of n into factors > 1, ordered by refinement.
%C A330935 This poset is equivalent to the poset of multiset partitions of the prime indices of n, ordered by refinement.
%F A330935 T(2^n,k) = A330785(n,k).
%F A330935 T(n,1) + T(n,2) = 1.
%e A330935 Triangle begins:
%e A330935    1:          16: 0 1 3 2    31: 1            46: 0 1
%e A330935    2: 1        17: 1          32: 0 1 5 8 4    47: 1
%e A330935    3: 1        18: 0 1 2      33: 0 1          48: 0 1 10 23 15
%e A330935    4: 0 1      19: 1          34: 0 1          49: 0 1
%e A330935    5: 1        20: 0 1 2      35: 0 1          50: 0 1 2
%e A330935    6: 0 1      21: 0 1        36: 0 1 7 7      51: 0 1
%e A330935    7: 1        22: 0 1        37: 1            52: 0 1 2
%e A330935    8: 0 1 1    23: 1          38: 0 1          53: 1
%e A330935    9: 0 1      24: 0 1 5 5    39: 0 1          54: 0 1 5 5
%e A330935   10: 0 1      25: 0 1        40: 0 1 5 5      55: 0 1
%e A330935   11: 1        26: 0 1        41: 1            56: 0 1 5 5
%e A330935   12: 0 1 2    27: 0 1 1      42: 0 1 3        57: 0 1
%e A330935   13: 1        28: 0 1 2      43: 1            58: 0 1
%e A330935   14: 0 1      29: 1          44: 0 1 2        59: 1
%e A330935   15: 0 1      30: 0 1 3      45: 0 1 2        60: 0 1 9 11
%e A330935 Row n = 48 counts the following chains (minimum and maximum not shown):
%e A330935   ()  (6*8)      (2*3*8)->(6*8)       (2*2*2*6)->(2*4*6)->(6*8)
%e A330935       (2*24)     (2*4*6)->(6*8)       (2*2*3*4)->(2*3*8)->(6*8)
%e A330935       (3*16)     (2*3*8)->(2*24)      (2*2*3*4)->(2*4*6)->(6*8)
%e A330935       (4*12)     (2*3*8)->(3*16)      (2*2*2*6)->(2*4*6)->(2*24)
%e A330935       (2*3*8)    (2*4*6)->(2*24)      (2*2*2*6)->(2*4*6)->(4*12)
%e A330935       (2*4*6)    (2*4*6)->(4*12)      (2*2*3*4)->(2*3*8)->(2*24)
%e A330935       (3*4*4)    (3*4*4)->(3*16)      (2*2*3*4)->(2*3*8)->(3*16)
%e A330935       (2*2*12)   (3*4*4)->(4*12)      (2*2*3*4)->(2*4*6)->(2*24)
%e A330935       (2*2*2*6)  (2*2*12)->(2*24)     (2*2*3*4)->(2*4*6)->(4*12)
%e A330935       (2*2*3*4)  (2*2*12)->(4*12)     (2*2*3*4)->(3*4*4)->(3*16)
%e A330935                  (2*2*2*6)->(6*8)     (2*2*3*4)->(3*4*4)->(4*12)
%e A330935                  (2*2*3*4)->(6*8)     (2*2*2*6)->(2*2*12)->(2*24)
%e A330935                  (2*2*2*6)->(2*24)    (2*2*2*6)->(2*2*12)->(4*12)
%e A330935                  (2*2*2*6)->(4*12)    (2*2*3*4)->(2*2*12)->(2*24)
%e A330935                  (2*2*3*4)->(2*24)    (2*2*3*4)->(2*2*12)->(4*12)
%e A330935                  (2*2*3*4)->(3*16)
%e A330935                  (2*2*3*4)->(4*12)
%e A330935                  (2*2*2*6)->(2*4*6)
%e A330935                  (2*2*3*4)->(2*3*8)
%e A330935                  (2*2*3*4)->(2*4*6)
%e A330935                  (2*2*3*4)->(3*4*4)
%e A330935                  (2*2*2*6)->(2*2*12)
%e A330935                  (2*2*3*4)->(2*2*12)
%t A330935 facs[n_]:=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[facs[n/d],Min@@#>=d&]],{d,Rest[Divisors[n]]}]];
%t A330935 upfacs[q_]:=Union[Sort/@Join@@@Tuples[facs/@q]];
%t A330935 paths[eds_,start_,end_]:=If[start==end,Prepend[#,{}],#]&[Join@@Table[Prepend[#,e]&/@paths[eds,Last[e],end],{e,Select[eds,First[#]==start&]}]];
%t A330935 Table[Length[Select[paths[Join@@Table[{y,#}&/@DeleteCases[upfacs[y],y],{y,facs[n]}],{n},First[facs[n]]],Length[#]==k-1&]],{n,100},{k,PrimeOmega[n]}]
%Y A330935 Row lengths are A001222.
%Y A330935 Row sums are A317176.
%Y A330935 Column k = 1 is A010051.
%Y A330935 Column k = 2 is A066247.
%Y A330935 Column k = 3 is A330936.
%Y A330935 Final terms of each row are A317145.
%Y A330935 The version for set partitions is A008826, with row sums A005121.
%Y A330935 The version for integer partitions is A330785, with row sums A213427.
%Y A330935 Cf. A001055, A002846, A003238, A007716, A281118, A292504, A292505, A318812, A330665, A330727.
%K A330935 nonn,tabf
%O A330935 1,19
%A A330935 _Gus Wiseman_, Jan 04 2020