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%I #13 Oct 13 2020 03:24:30
%S 3,2,6,5,10,1,3,-3,2,-1,4,-4,5,-2,7,4,6,3,11,7,13,11,17,13,16,13,21,
%T 18,20,13,22,17,17,15,23,15,19,18,27,20,21,15,24,21,30,21,24,17,22,21,
%U 21,16,24,22,22,13,20,16,25,21,25,20,29,27,30,30,37,29,30
%N a(n) = d(1) - d(2) + d(3) - d(4) + ... + (-1)^(n+1) d(n), where d(k) denotes the k-th term of the digit sequence 3, 1, 4, 1, 5, 9,.... of Pi.
%H Amiram Eldar, <a href="/A069159/b069159.txt">Table of n, a(n) for n = 1..10000</a>
%H Kevin S. Brown, <a href="http://www.mathpages.com/home/kmath369.htm">Random Walk Through Pi</a>.
%F a(1) = d(1) = 3; a(n) = a(n-1) + (-1)^(n+1) d(n) for n > 1.
%e a(3) = d(1) - d(2) + d(3) = 3 - 1 + 4 = 6.
%t n = 100; Accumulate[(-1)^Range[0, n - 1] * RealDigits[Pi, 10, n][[1]]] (* _Amiram Eldar_, Oct 13 2020 *)
%Y Cf. A000796 (Pi).
%K base,easy,sign
%O 1,1
%A _Joseph L. Pe_, Apr 09 2002
%E More terms from _Amiram Eldar_, Oct 13 2020