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 A254865 a(n) = Product_{k = 1+n-floor(n/3) .. n} k. 2
 1, 1, 3, 4, 5, 30, 42, 56, 504, 720, 990, 11880, 17160, 24024, 360360, 524160, 742560, 13366080, 19535040, 27907200, 586051200, 859541760, 1235591280, 29654190720, 43609104000, 62990928000, 1700755056000, 2506375872000, 3634245014400, 109027350432000, 160945136352000, 234102016512000, 7725366544896000, 11420107066368000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Informally: Take the upper third of natural numbers in range [1..n] and multiply them together. LINKS FORMULA a(n) = Product_{k = 1+n-floor(n/3) .. n} k. Other identities. For all n >= 1: a(3n) = A064352(n). PROG (Scheme) (define (A254865 n) (mul A000027 (+ 1 (- n (floor->exact (/ n 3)))) n)) (define (mul intfun lowlim uplim) (let multloop ((i lowlim) (res 1)) (cond ((> i uplim) res) (else (multloop (+ 1 i) (* res (intfun i))))))) (define (A254865 n) (A254864bi n 1)) ;; Alternatively, using code given in A254864. CROSSREFS Leftmost column of A254864. Trisection: A064352. Sequence in context: A123957 A085285 A282250 * A085841 A163483 A004784 Adjacent sequences:  A254862 A254863 A254864 * A254866 A254867 A254868 KEYWORD nonn AUTHOR Antti Karttunen, Feb 09 2015 STATUS approved

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Last modified September 15 16:12 EDT 2019. Contains 327078 sequences. (Running on oeis4.)