A141267 Concatenate first n double factorials in reverse order.

1, 21, 321, 8321, 158321, 48158321, 10548158321, 38410548158321, 94538410548158321, 384094538410548158321, 10395384094538410548158321, 4608010395384094538410548158321, 1351354608010395384094538410548158321

Offset

0,2

Links

Table of n, a(n) for n=0..12.

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

Cf. A045508, A141265, A141266.

Sequence in context: A060554 A057610 A036737 * A346321 A016262 A001233

Adjacent sequences: A141264 A141265 A141266 * A141268 A141269 A141270

Keyword

nonn,base

Author

Paolo P. Lava, Jun 20 2008

Status

approved