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%I #31 Mar 10 2020 12:55:34
%S 3,1,4,1,6,3,2,5,6,0,6,5,5,1,5,3,8,6,6,2,9,3,8,4,2,7,7,0,2,2,5,4,2,9,
%T 4,3,4,2,2,6,0,6,1,5,3,7,9,5,6,7,3,9,7,4,7,8,0,4,6,5,1,6,2,2,3,8,0,1,
%U 4,4,6,0,3,7,3,3,3,5,1,7,7,5,6,0,0,3,6,4,1,7,1,6,2,3,3,5,9,1,3,3,0,8,6
%N Decimal expansion of (1/2) * (1 + 2/1 + 4/(2*1) + 8/(4*2*1) + ... ).
%C An approximation to Pi.
%F Equals (1/2)*Sum_{k>=0} 2^(k-binomial(k,2)). - _Andrew Howroyd_, Feb 21 2020
%F Equals A190405 +2.5 = A299998 +1.5. All digits the same but the first one or two. - _R. J. Mathar_, Mar 10 2020
%e 3.1416325606551538662938427702254294342260615379567...
%p c:= sum(2^(j*(3-j)/2-1), j=0..infinity):
%p evalf(c, 125); # _Alois P. Heinz_, Mar 03 2020
%o (PARI) suminf(k=0, 2^(k-binomial(k,2)-1)) \\ _Andrew Howroyd_, Feb 21 2020
%Y Cf. A000796 (Pi), A013705.
%K nonn,cons
%O 1,1
%A _Drew Edgette_, Feb 19 2020
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