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A280881
Number of set partitions of [n] into exactly three blocks where sizes of distinct blocks are coprime.
2
1, 6, 10, 75, 21, 476, 540, 4185, 1375, 47850, 10374, 249431, 395955, 2572680, 278392, 30877389, 5000211, 214159070, 291693150, 1465649955, 1224138223, 23284864476, 13175039700, 157019230225, 198060711381, 1510657970346, 1118209769530, 18176060999625
OFFSET
3,2
LINKS
EXAMPLE
a(3) = 1: 1|2|3.
a(4) = 6: 12|3|4, 13|2|4, 1|23|4, 14|2|3, 1|24|3, 1|2|34.
a(5) = 10: 123|4|5, 124|3|5, 125|3|4, 134|2|5, 135|2|4, 1|234|5, 1|235|4, 145|2|3, 1|245|3, 1|2|345.
a(7) = 21: 12345|6|7, 12346|5|7, 12347|5|6, 12356|4|7, 12357|4|6, 12367|4|5, 12456|3|7, 12457|3|6, 12467|3|5, 12567|3|4, 13456|2|7, 13457|2|6, 13467|2|5, 13567|2|4, 1|23456|7, 1|23457|6, 1|23467|5, 1|23567|4, 14567|2|3, 1|24567|3, 1|2|34567.
CROSSREFS
Column k=3 of A280880.
Sequence in context: A119041 A105157 A166386 * A256246 A246800 A269341
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jan 09 2017
STATUS
approved