A004781 Binary expansion contains 3 adjacent 1's.

7, 14, 15, 23, 28, 29, 30, 31, 39, 46, 47, 55, 56, 57, 58, 59, 60, 61, 62, 63, 71, 78, 79, 87, 92, 93, 94, 95, 103, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 135, 142, 143, 151, 156, 157, 158, 159, 167

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• base
• easy

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Index entries for 2-automatic sequences.

Crossrefs

Complement of A003726.

Cf. A004779, A136037.

Programs

Haskell

a004781 n = a004781_list !! (n - 1)
a004781_list = filter f [0..] where
   f x | x < 7     = False
       | otherwise = (x `mod` 8) == 7 || f (x `div` 2)
-- Reinhard Zumkeller, Jun 03 2012

Maple

q:= n-> verify([1$3], Bits[Split](n), 'sublist'):
select(q, [$0..200])[];  # Alois P. Heinz, Oct 22 2021

Mathematica

Select[Range[200],MemberQ[Partition[IntegerDigits[#,2],3,1], {1,1,1}]&]  (* Harvey P. Dale, Mar 31 2011 *)
Select[Range[200], StringContainsQ[IntegerString[#, 2], "111"] &] (* Amiram Eldar, Oct 22 2021 *)
Select[Range[200],SequenceCount[IntegerDigits[#,2],{1,1,1}]>0&] (* Harvey P. Dale, Dec 28 2021 *)

PARI

is(n)=!!bitand(bitand(n,n<<1),n<<2) \\ Charles R Greathouse IV, Sep 24 2012

Formula

a(n) ~ n. - Charles R Greathouse IV, Sep 24 2012

Extensions

Offset corrected by Reinhard Zumkeller, Jun 03 2012