A261396 - OEIS

%I #19 Aug 31 2015 21:38:41

%S 1,2,3,4,7,12,19,34,61,110,200,371,697,1310,2484,4739,9072,17458,

%T 33671,65128,126225,244802,475124,922891,1793461,3487348,6784691,

%U 13208038,25731600,50166771,97873783,191089176,373349780,729972649,1428257200,2796453078,5478981032,10741710906,21072415837

%N a(n) = smallest k such that A260273(k) >= 2^n.

%C The sequence indicates the first time a term in A260273 has binary length n+1.

%C A261646 = first differences = row lengths of tables A261644 and A261712. - _Reinhard Zumkeller_, Aug 30 2015

%o (Haskell)

%o a261396 n = a261396_list !! (n-1)

%o a261396_list = f 1 1 a260273_list where

%o    f z k (x:xs) | x >= z    = k : f (2 * z) (k + 1) xs

%o                 | otherwise = f z (k + 1) xs

%o -- _Reinhard Zumkeller_, Aug 30 2015

%Y Cf. A260273.

%Y Cf. A261646, A261644, A261712.

%K nonn

%O 0,2

%A _N. J. A. Sloane_, Aug 17 2015

%E a(18)-a(23) from _Alois P. Heinz_, Aug 19 2015

%E a(24)-a(34) from _Chai Wah Wu_, Aug 26 2015

%E a(35)-a(38) from _Chai Wah Wu_, Aug 31 2015