cp's OEIS Frontend

A004094 Powers of 2 written backwards.

%I A004094 #50 Jan 07 2025 02:01:00
%S A004094 1,2,4,8,61,23,46,821,652,215,4201,8402,6904,2918,48361,86723,63556,
%T A004094 270131,441262,882425,6758401,2517902,4034914,8068838,61277761,
%U A004094 23445533,46880176,827712431,654534862,219078635,4281473701,8463847412,6927694924,2954399858,48196897171
%N A004094 Powers of 2 written backwards.
%C A004094 Freeman Dyson believes that A014963(a(n)) <> 5 is true but cannot be proved, see link. - _Reinhard Zumkeller_, Jan 05 2005
%H A004094 T. D. Noe, <a href="/A004094/b004094.txt">Table of n, a(n) for n = 0..1000</a>
%H A004094 Edge Foundation, <a href="https://www.edge.org/response-detail/11675">Annual Question 2005</a>
%H A004094 Richard Lipton, <a href="https://rjlipton.wordpress.com/2014/10/11/more-on-testing-dysons-conjecture/">More on testing Dyson's conjecture</a> (2014)
%H A004094 N. J. A. Sloane, <a href="https://www.youtube.com/watch?v=9ogbsh8KuEM">Exciting Number Sequences</a> (video of talk), Mar 05 2021.
%F A004094 a(n) = A004086(A000079(n)). - _Reinhard Zumkeller_, Apr 02 2014
%p A004094 a:= n-> (s-> parse(cat(s[-i]$i=1..length(s))))(""||(2^n)):
%p A004094 seq(a(n), n=0..50);  # _Alois P. Heinz_, Jan 21 2020
%t A004094 Table[FromDigits[Reverse[IntegerDigits[2^n]]], {n, 0, 35}] (* _Vincenzo Librandi_, Jan 22 2020 *)
%o A004094 (Haskell)
%o A004094 a004094 = a004086 . a000079  -- _Reinhard Zumkeller_, Apr 02 2014
%o A004094 (PARI) rev(n)=subst(Polrev(digits(n)),'x,10)
%o A004094 a(n)=rev(2^n) \\ _Charles R Greathouse IV_, Oct 20 2014
%o A004094 (PARI) apply( {A004094(n)=fromdigits(Vecrev(digits(2^n)))}, [0..44]) \\ _M. F. Hasler_, Feb 18 2021
%o A004094 (Magma) [Seqint(Reverse(Intseq(2^n))): n in [0..35]]; // _Vincenzo Librandi_, Jan 22 2020
%o A004094 (Python)
%o A004094 def A004094(n):
%o A004094     return int(str(2**n)[::-1]) # _Chai Wah Wu_, Feb 19 2021
%Y A004094 Cf. A014963, A102382, A102383, A102384, A102385.
%Y A004094 The following are parallel families: A000079 (2^n), A004094 (2^n reversed), A028909 (2^n sorted up), A028910 (2^n sorted down), A036447 (double and reverse), A057615 (double and sort up), A263451 (double and sort down); A000244 (3^n), A004167 (3^n reversed), A321540 (3^n sorted up), A321539 (3^n sorted down), A163632 (triple and reverse), A321542 (triple and sort up), A321541 (triple and sort down).
%Y A004094 Cf. A004086 (read n backwards).
%Y A004094 For indices of primes see A057708.
%K A004094 nonn,base,easy
%O A004094 0,2
%A A004094 _N. J. A. Sloane_
%E A004094 More terms from _Reinhard Zumkeller_, Jan 05 2005