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a(n) = k-1, where k is smallest number such that A002487(k) = n.
10

%I #10 May 05 2023 12:29:47

%S 0,2,4,8,10,32,18,20,34,38,36,44,42,68,72,92,76,74,82,188,84,140,138,

%T 152,150,146,154,266,148,164,172,278,274,170,282,314,276,536,324,296,

%U 292,578,300,308,364,332,298,566,330,338,552,548,562,1274,340,584,564,614,628

%N a(n) = k-1, where k is smallest number such that A002487(k) = n.

%e A002487(33) = 6 and this is the first time 6 appears, so a(6) = 33-1 = 32.

%o (Python)

%o from itertools import count

%o from functools import reduce

%o def A020950(n): return next(filter(lambda k:sum(reduce(lambda x,y:(x[0],x[0]+x[1]) if int(y) else (x[0]+x[1],x[1]),bin(k)[-1:2:-1],(1,0)))==n,count(1)))-1 # _Chai Wah Wu_, May 05 2023

%Y Equals A020946 - 1.

%Y Cf. A020943-A020946, A002487, A020947-A020949.

%K nonn

%O 1,2

%A _Clark Kimberling_

%E Corrected and extended by _David W. Wilson_