A342338 Number of compositions of n with all adjacent parts (x, y) satisfying x < 2y and y <= 2x.

1, 1, 2, 3, 4, 6, 8, 12, 17, 24, 34, 51, 73, 106, 155, 224, 328, 477, 695, 1013, 1477, 2154, 3140, 4578, 6673, 9728, 14176, 20663, 30113, 43882, 63940, 93167, 135747, 197776, 288138, 419773, 611522, 890829, 1297685, 1890305, 2753505, 4010804, 5842113, 8509462

Offset

0,3

Comments

Also the number of compositions of n with all adjacent parts (x, y) satisfying x <= 2y and y < 2x.

Links

Andrew Howroyd, Table of n, a(n) for n = 0..1000

Example

The a(1) = 1 through a(7) = 12 compositions:
  (1)  (2)   (3)    (4)     (5)      (6)       (7)
       (11)  (21)   (22)    (23)     (33)      (34)
             (111)  (211)   (32)     (42)      (43)
                    (1111)  (221)    (222)     (223)
                            (2111)   (321)     (232)
                            (11111)  (2211)    (322)
                                     (21111)   (421)
                                     (111111)  (2221)
                                               (3211)
                                               (22111)
                                               (211111)
                                               (1111111)

Mathematica

Table[Length[Select[Join@@Permutations/@IntegerPartitions[n], And@@Table[#[[i]]<2*#[[i-1]]&&#[[i-1]]<=2*#[[i]], {i, 2, Length[#]}]&]], {n, 0, 15}]
(* Second program: *)
c[n_, pred_] := Module[{M = IdentityMatrix[n], i, k}, For[k = 1, k <= n, k++, For[i = 1, i <= k - 1, i++, M[[i, k]] = Sum[If[pred[j, i], M[[j, k - i]], 0], {j, 1, k - i}]]]; Sum[M[[q, All]], {q, 1, n}]];
pred[i_, j_] := i < 2j && j <= 2i;
Join[{1}, c[60, pred]] (* Jean-François Alcover, Jun 10 2021, after Andrew Howroyd *)

Prog

(PARI)
C(n, pred)={my(M=matid(n)); for(k=1, n, for(i=1, k-1, M[i, k]=sum(j=1, k-i, if(pred(j, i), M[j, k-i], 0)))); sum(q=1, n, M[q, ])}
seq(n)={concat([1], C(n, (i, j)->i<2*j && j<=2*i))} \\ Andrew Howroyd, Mar 13 2021

Crossrefs

The first condition alone gives A274199.

The second condition alone gives A002843.

Reversing operators and changing 'and' to 'or' gives A342334.

The version with both relations strict is A342341.

The version with neither relation strict is A342342.

A000929 counts partitions with adjacent parts x >= 2y.

A002843 counts compositions with adjacent parts x <= 2y.

A154402 counts partitions with adjacent parts x = 2y.

A224957 counts compositions with x <= 2y and y <= 2x.

A274199 counts compositions with adjacent parts x < 2y.

A342094 counts partitions with adjacent x <= 2y (strict: A342095).

A342096 counts partitions without adjacent x >= 2y (strict: A342097).

A342098 counts partitions with adjacent parts x > 2y.

A342330 counts compositions with x < 2y and y < 2x.

A342331 counts compositions with adjacent parts x = 2y or y = 2x.

A342332 counts compositions with adjacent parts x > 2y or y > 2x.

A342333 counts compositions with adjacent parts x >= 2y or y >= 2x.

A342335 counts compositions with adjacent parts x >= 2y or y = 2x.

A342337 counts partitions with adjacent parts x = y or x = 2y.

Cf. A003114, A003242, A034296, A167606, A342083, A342084, A342087, A342191, A342336, A342340.

Sequence in context: A306201 A218935 A018438 * A221942 A107368 A074733

Adjacent sequences: A342335 A342336 A342337 * A342339 A342340 A342341

Keyword

nonn

Author

Gus Wiseman, Mar 11 2021

Extensions

Terms a(21) and beyond from Andrew Howroyd, Mar 13 2021

Status

approved