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A346636 a(n) is the number of quadruples (a_1, a_2, a_3, a_4) having all terms in {1,...,n} such that there exists a quadrilateral with these side lengths. 3
0, 1, 16, 77, 236, 565, 1156, 2121, 3592, 5721, 8680, 12661, 17876, 24557, 32956, 43345, 56016, 71281, 89472, 110941, 136060, 165221, 198836, 237337, 281176, 330825, 386776, 449541, 519652, 597661, 684140, 779681, 884896, 1000417, 1126896, 1265005, 1415436 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
The existence of such a four-sided polygon implies that every element of the quadruple is less than the sum of the other elements.
LINKS
Sean A. Irvine, Java program (github)
FORMULA
Formula: a(n) = n^4 - 4*binomial(n+1,4) = n^4 - (n+1)*binomial(n,3).
General formula for k-tuples: a_k(n) = n^k - k*binomial(n+1,k) = n^k - (n+1)*binomial(n,k-1).
PROG
(Visual Basic) ' See Links.
CROSSREFS
Sequence in context: A300919 A007834 A228741 * A200873 A082966 A198182
KEYWORD
nonn
AUTHOR
Giovanni Corbelli, Jul 26 2021
STATUS
approved

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Last modified April 16 23:10 EDT 2024. Contains 371755 sequences. (Running on oeis4.)