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A185348 Number of ordered quadruples of distinct pairwise coprime positive integers with largest element n; also first differences of A015623. 4
0, 0, 0, 0, 2, 0, 8, 4, 10, 2, 42, 4, 79, 16, 25, 36, 183, 20, 277, 50, 100, 70, 491, 56, 399, 139, 340, 146, 1016, 56, 1285, 398, 493, 342, 706, 184, 2150, 501, 807, 363, 2968, 210, 3522, 775, 935, 904, 4620, 508, 3732, 842, 2011, 1255, 6684, 728, 3355, 1304, 2785, 1877, 9141, 546 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..1000

EXAMPLE

a(4) = 0 because there is only one ordered quadruple of distinct positive integers with largest element 4, (1,2,3,4), but the elements are not pairwise coprime, 2 and 4 have a common factor >1.

a(8) = 4 because there are only four ordered quadruples of distinct pairwise coprime positive integers with largest element 8: (1,3,5,8), (1,3,7,8), (1,5,7,8), (3,5,7,8).

CROSSREFS

Cf. A015623, A185953. Column 4 of triangle A186972.

Sequence in context: A252852 A099380 A154909 * A321599 A020780 A334071

Adjacent sequences:  A185345 A185346 A185347 * A185349 A185350 A185351

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Feb 15 2011

STATUS

approved

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Last modified July 25 02:37 EDT 2021. Contains 346276 sequences. (Running on oeis4.)