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A141267
Concatenate first n double factorials in reverse order.
2
1, 21, 321, 8321, 158321, 48158321, 10548158321, 38410548158321, 94538410548158321, 384094538410548158321, 10395384094538410548158321, 4608010395384094538410548158321, 1351354608010395384094538410548158321
OFFSET
0,2
FORMULA
a(n) = n!!*10^floor(1+log_10(a(n-1))) + a(n-1), with a(1)=1.
MAPLE
P:=proc(i) local a, j, k, n; a:=1; print(1); for n from 2 by 1 to i do k:=n; j:=n-2; while j>0 do k:=k*j; j:=j-2; od; a:=k*10^floor(evalf(1+log10(a), 1000))+a; print(a); od; end: P(20);
MATHEMATICA
FromDigits/@(Flatten[IntegerDigits/@Reverse[#]]&/@Table[ Take[Range[20]!!, n], {n, 20}]) (* Harvey P. Dale, Sep 30 2011 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava, Jun 20 2008
STATUS
approved