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A238957
The number of nodes at even level in divisor lattice in graded colexicographic order.
3
1, 1, 2, 2, 2, 3, 4, 3, 4, 5, 6, 8, 3, 5, 6, 8, 9, 12, 16, 4, 6, 8, 8, 10, 12, 14, 16, 18, 24, 32, 4, 7, 9, 10, 12, 15, 16, 18, 20, 24, 27, 32, 36, 48, 64, 5, 8, 11, 12, 13, 14, 18, 20, 23, 24, 24, 30, 32, 36, 41, 40, 48, 54, 64, 72, 96, 128
OFFSET
0,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..2713 (rows 0..20)
S.-H. Cha, E. G. DuCasse, and L. V. Quintas, Graph Invariants Based on the Divides Relation and Ordered by Prime Signatures, arxiv:1405.5283 [math.NT], 2014.
FORMULA
T(n,k) = A038548(A036035(n,k)).
From Andrew Howroyd, Apr 01 2020: (Start)
T(n,k) = A074139(n,k) - A238958(n,k).
T(n,k) = ceiling(A074139(n,k)/2). (End)
EXAMPLE
Triangle T(n,k) begins:
1;
1;
2, 2;
2, 3, 4;
3, 4, 5, 6, 8;
3, 5, 6, 8, 9, 12, 16;
4, 6, 8, 8, 10, 12, 14, 16, 18, 24, 32;
...
PROG
(PARI) \\ here b(n) is A038548.
b(n)={ceil(numdiv(n)/2)}
N(sig)={prod(k=1, #sig, prime(k)^sig[k])}
Row(n)={apply(s->b(N(s)), [Vecrev(p) | p<-partitions(n)])}
{ for(n=0, 8, print(Row(n))) } \\ Andrew Howroyd, Apr 01 2020
CROSSREFS
Cf. A038548 in graded colexicographic order.
Sequence in context: A362739 A112184 A112213 * A238970 A085755 A330216
KEYWORD
nonn,tabf
AUTHOR
Sung-Hyuk Cha, Mar 07 2014
EXTENSIONS
Offset changed and terms a(50) and beyond from Andrew Howroyd, Apr 01 2020
STATUS
approved