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 A084940 Heptagorials: n-th polygorial for k=7. 20
 1, 1, 7, 126, 4284, 235620, 19085220, 2137544640, 316356606720, 59791398670080, 14050978687468800, 4018579904616076800, 1374354327378698265600, 553864793933615401036800, 259762588354865623086259200 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Daniel Dockery, Polygorials, Special "Factorials" of Polygonal Numbers, preprint, 2003. FORMULA a(n) = polygorial(n, 7) = (A000142(n)/A000079(n))*A047055(n) = (n!/2^n)*Product_{i=0..n-1}(5*i+2) = (n!/2^n)*5^n*Pochhammer(2/5, n) = (n!/2^n)*5^n*GAMMA(n+2/5)*sin(2*Pi/5)*GAMMA(3/5)/Pi. 2*a(n) = n*(5*n-3)*a(n-1). - R. J. Mathar, Mar 12 2019 MAPLE a := n->n!/2^n*mul(5*i+2, i=0..n-1); [seq(a(j), j=0..30)]; MATHEMATICA polygorial[k_, n_] := FullSimplify[ n!/2^n (k -2)^n*Pochhammer[2/(k -2), n]]; Array[ polygorial[7, #] &, 16, 0] (* Robert G. Wilson v, Dec 26 2016 *) Join[{1}, FoldList[Times, PolygonalNumber[7, Range[20]]]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 29 2019 *) PROG (PARI) a(n)=n!/2^n*prod(i=1, n, 5*i-3) \\ Charles R Greathouse IV, Dec 13 2016 CROSSREFS Cf. A006472, A001044, A000680, A084939, A084941, A084942, A084943, A084944, A085356. Sequence in context: A295412 A202798 A204248 * A246648 A308378 A139987 Adjacent sequences:  A084937 A084938 A084939 * A084941 A084942 A084943 KEYWORD easy,nonn AUTHOR Daniel Dockery (peritus(AT)gmail.com), Jun 13 2003 STATUS approved

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Last modified October 23 09:28 EDT 2019. Contains 328345 sequences. (Running on oeis4.)