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A358990
a(n) is the product of the first n odd numbers not divisible by 5.
3
1, 1, 3, 21, 189, 2079, 27027, 459459, 8729721, 183324141, 4216455243, 113844291561, 3301484455269, 102346018113339, 3377418597740187, 124964488116386919, 4873615036539089841, 199818216498102683481, 8592183309418415389683, 403832615542665523315101, 19787798161590610642439949
OFFSET
0,3
COMMENTS
Unlike the factorial number n!, but like A356858(n), a(n) does not have trailing zeros.
FORMULA
a(n) = Product_{k=1..n} A045572(k).
MATHEMATICA
Table[Product[2*k+2*Floor[(k-3)/4]+1, {k, n}], {n, 0, 20}]
PROG
(PARI) f(n) = 2*n - 1 + (n+1)\4 * 2; \\ A045572
a(n) = prod(k=1, n, f(k)); \\ Michel Marcus, Dec 10 2022
CROSSREFS
Cf. A358991 (number of zero digits), A358992 (number of digits), A358993 (number of nonzero digits).
Sequence in context: A012163 A012055 A344896 * A059863 A256625 A057616
KEYWORD
nonn
AUTHOR
Stefano Spezia, Dec 09 2022
STATUS
approved