OFFSET
1,1
COMMENTS
Numbers 2*m such that floor(f(m))=floor(f(m-1)) where f(m)= Sum_{j=1..m} ((2*j-1)/(2*j)). Examples: floor(f(1))=floor(1/2)=0; floor(f(2))=floor(1/2+2/3)=floor(1,25)=1, then 2*2=4 is not in the sequence; floor(f(3))=floor((1/2+3/4+4/5)=floor(2,083..)=2, then 2*3=6 is not in the sequence; floor((f(4))=floor(1/2+3/4+5/6+7/8)=floor(2,958..)=2, then 2*4=8 is the first term of the sequence. - Philippe Lallouet (philip.lallouet(AT)wanadoo.fr), Aug 15 2007
REFERENCES
Calvin C. Clawson, Mathematical Mysteries, The Beauty and Magic of Numbers, Plenum Press, NY and London, 1996, page 64.
FORMULA
a(n) = 2*A002387(2n).
The next term is approximately the previous term * e^2.
MATHEMATICA
s = 0; k = 2; Do[ While[s = N[s + 1/k, 24]; s <= n, k += 2]; Print[k]; k += 2, {n, 1, 12}]
(* or assuming that the Mathematica coding in A002387 is correct then *)
b[n_] := Module[{k = Floor[2a[2n]]}, If[ EvenQ[k], k, k + 1]]; Table[ b[n], {n, 19}] (* Robert G. Wilson v, Apr 17 2004 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Jul 25 2000 and Jan 11 2004
STATUS
approved