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A137989
Decimal expansion of the inverse of the number whose Engel expansion has the sequence of double factorial numbers (A000165) as coefficients.
5
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
OFFSET
0,1
LINKS
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
KEYWORD
easy,nonn,cons
AUTHOR
STATUS
approved