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A241692
Number of Carlitz compositions of n with exactly two descents.
2
2, 5, 12, 27, 53, 98, 174, 296, 486, 781, 1222, 1874, 2827, 4195, 6138, 8873, 12675, 17918, 25095, 34832, 47954, 65529, 88911, 119842, 160552, 213841, 283266, 373318, 489601, 639149, 830750, 1075292, 1386313, 1780572, 2278703, 2906137, 3694123, 4680892
OFFSET
6,1
COMMENTS
No two adjacent parts of a Carlitz composition are equal.
LINKS
MAPLE
b:= proc(n, i) option remember; `if`(n=0, 1,
convert(series(add(`if`(i=j, 0, b(n-j, j)*
`if`(j<i, x, 1)), j=1..n), x, 3), polynom))
end:
a:= n-> coeff(b(n, 0), x, 2):
seq(a(n), n=6..50);
CROSSREFS
Column k=2 of A241701.
Sequence in context: A221950 A116716 A128812 * A078410 A096766 A362193
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Apr 27 2014
STATUS
approved