A132852 Number of sequences {c(i), i=0..n} that form the initial terms of a self-convolution square of an integer sequence such that 0 < c(n) <= 2*c(n-1) for n>0 with c(0)=1.

1, 1, 2, 4, 14, 62, 462, 5380, 105626, 3440686, 196429906, 19603795552, 3496015313038, 1120368106124268, 653253602487886098, 697073727912597623594, 1371575342274982257650434

Offset

0,3

Comments

Equals the number of nodes at generation n in the 2-convoluted tree. The minimal path in the 2-convoluted tree is A083952 and the maximal path is A132831. The 2-convoluted tree is defined as follows: tree of all finite sequences {c(k), k=0..n} that form the initial terms of a self-convolution square of some integer sequence such that 0 < c(n) <= 2*c(n-1) for n>0 with a(0)=1.

Links

Table of n, a(n) for n=0..16.

Martin Fuller, Computing A132852, A132853, A132854, A132855, A132856

Example

a(n) counts the nodes in generation n of the following tree.
Generations 0..5 of the 2-convoluted tree are as follows;
The path from the root is shown, with child nodes enclosed in [].
GEN.0: [1];
GEN.1: 1->[2];
GEN.2: 1-2->[1,3];
GEN.3:
1-2-1->[2]
1-2-3->[2,4,6];
GEN.4:
1-2-1-2->[2,4]
1-2-3-2->[1,3]
1-2-3-4->[1,3,5,7]
1-2-3-6->[1,3,5,7,9,11];
GEN.5:
1-2-1-2-2->[2,4]
1-2-1-2-4->[2,4,6,8]
1-2-3-2-1->[2]
1-2-3-2-3->[2,4,6]
1-2-3-4-1->[2]
1-2-3-4-3->[2,4,6]
1-2-3-4-5->[2,4,6,8,10]
1-2-3-4-7->[2,4,6,8,10,12,14]
1-2-3-6-1->[2]
1-2-3-6-3->[2,4,6]
1-2-3-6-5->[2,4,6,8,10]
1-2-3-6-7->[2,4,6,8,10,12,14]
1-2-3-6-9->[2,4,6,8,10,12,14,16,18]
1-2-3-6-11->[2,4,6,8,10,12,14,16,18,20,22].
Each path in the tree from the root node forms the initial terms of a self-convolution square of a sequence with integer terms.

Crossrefs

Cf. A132853, A132854, A132855, A132856.

Cf. A083952, A132831.

Sequence in context: A019537 A046911 A089127 * A352644 A132079 A055790

Adjacent sequences: A132849 A132850 A132851 * A132853 A132854 A132855

Keyword

nonn

Author

Paul D. Hanna, Sep 19 2007, Oct 06 2007

Extensions

Extended by Martin Fuller, Sep 24 2007.

Status

approved