A137989 - OEIS

A137989

Decimal expansion of the inverse of the number whose Engel expansion has the sequence of double factorial numbers (A000165) as coefficients.

3, 7, 1, 8, 9, 6, 7, 8, 6, 2, 4, 4, 2, 5, 5, 8, 4, 7, 8, 3, 9, 5, 5, 1, 5, 3, 1, 1, 0, 6, 8, 3, 4, 0, 0, 3, 3, 4, 4, 1, 4, 2, 1, 6, 5, 0, 6, 7, 9, 1, 3, 0, 0, 2, 2, 8, 1, 1, 2, 5, 3, 9, 1, 1, 3, 8, 9, 3, 4, 8, 3, 0, 4, 4, 4, 1, 7, 6, 7, 7, 6, 4, 3, 0, 9, 3, 0, 2, 6, 3, 3, 1, 0, 7, 2, 5, 3, 6, 5

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OFFSET

0,1

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..5000

Eric W. Weisstein, Pierce Expansion.

Eric W. Weisstein, Engel Expansion.

MAPLE

P:=proc(n) local a, i, j, k, w; a:=0; w:=1; for i from 0 by 1 to n do k:=i; j:=i-2; while j>0 do k:=k*j; j:=j-2; od; if (i=0 or i=1) then k:=1; fi; if i=2 then k:=2; fi; w:=w*k; a:=a+1/w; print(evalf(1/a, 100)); od; end: P(100);

MATHEMATICA

RealDigits[N[(1/Sum[Product[1/((k - 1)!!), {k, 1, n}], {n, 1, 250}]), 100]][[1]] (* G. C. Greubel, Jan 01 2016 *)

CROSSREFS

Cf. A000142, A137986, A137987, A137988.

Sequence in context: A197021 A291858 A355417 * A329286 A191335 A338366

Adjacent sequences: A137986 A137987 A137988 * A137990 A137991 A137992

KEYWORD

easy,nonn,cons

AUTHOR

Paolo P. Lava and Giorgio Balzarotti, Feb 26 2008

STATUS

approved