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Numbers whose decimal expansion contains only 0's and 5's.
17

%I #27 Oct 30 2023 11:35:31

%S 0,5,50,55,500,505,550,555,5000,5005,5050,5055,5500,5505,5550,5555,

%T 50000,50005,50050,50055,50500,50505,50550,50555,55000,55005,55050,

%U 55055,55500,55505,55550,55555,500000,500005,500050,500055,500500,500505,500550,500555

%N Numbers whose decimal expansion contains only 0's and 5's.

%H Reinhard Zumkeller, <a href="/A169964/b169964.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Ca#CARRYLESS">Index entries for sequences related to carryless arithmetic</a>

%F a(n+1) = Sum_{k>=0} A030308(n,k)*A093143(k+1). - _Philippe Deléham_, Oct 16 2011

%F a(n) = 5 * A007088(n-1).

%t Map[FromDigits,Tuples[{0,5},6]] (* _Paolo Xausa_, Oct 30 2023 *)

%o (PARI) print1(0);for(d=1,5,for(n=2^(d-1),2^d-1,print1(", ");forstep(i=d-1,0,-1,print1((n>>i)%2*5)))) \\ _Charles R Greathouse IV_, Nov 16 2011

%o (Haskell)

%o a169964 n = a169964_list !! (n-1)

%o a169964_list = map (* 5) a007088_list

%o -- _Reinhard Zumkeller_, Jan 10 2012

%Y Cf. A007088, A014263, A169965, A169966, A169967.

%Y Cf. A078244, A204093, A204094, A204095, A097256.

%K nonn,base,easy

%O 1,2

%A _N. J. A. Sloane_, Aug 07 2010