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A336743
a(n) is the product of the first n positive evil numbers.
0
1, 3, 15, 90, 810, 8100, 97200, 1458000, 24786000, 446148000, 8922960000, 205228080000, 4925473920000, 132987795840000, 3856646079360000, 115699382380800000, 3818079618566400000, 129814707031257600000, 4673329453125273600000, 182259848671885670400000
OFFSET
0,2
COMMENTS
Despite 0 appearing in the evil numbers, it is excluded here for obvious reasons.
This sequence features a mixture of odious and evil numbers, demonstrated in terms such as a(5) and a(8), where 8100 is evil but 24768000 is odious. As such, this shows that despite doubling preserving evilness, this is untrue for all multipliers.
FORMULA
a(n) = Product_{k=2, n+1} A001969(k). - Michel Marcus, Sep 27 2020
EXAMPLE
a(3) = 3*5*6 = 90.
a(8) = 3*5*6*9*10*12*15*17 = 24786000.
MATHEMATICA
FoldList[Times, 1, Select[Range[40], EvenQ @ DigitCount[#, 2, 1] &]] (* Amiram Eldar, Sep 26 2020 *)
CROSSREFS
Cf. A000142, A000069 (odious), A001969 (evil).
Sequence in context: A185369 A024339 A319950 * A374657 A034954 A077783
KEYWORD
nonn,base
AUTHOR
STATUS
approved