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A004094
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Powers of 2 written backwards.
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28
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1, 2, 4, 8, 61, 23, 46, 821, 652, 215, 4201, 8402, 6904, 2918, 48361, 86723, 63556, 270131, 441262, 882425, 6758401, 2517902, 4034914, 8068838, 61277761, 23445533, 46880176, 827712431, 654534862, 219078635, 4281473701, 8463847412
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refs;
listen;
history;
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internal format)
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OFFSET
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0,2
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COMMENTS
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Freeman Dyson believes that A014963(a(n)) <> 5 is true but cannot be proved, see link. - Reinhard Zumkeller, Jan 05 2005
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LINKS
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T. D. Noe, Table of n, a(n) for n = 0..1000
Edge Foundation, Annual Question 2005
Richard Lipton, More on testing Dyson's conjecture (2014)
N. J. A. Sloane, Exciting Number Sequences (video of talk), Mar 05 2021.
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FORMULA
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a(n) = A004086(A000079(n)). - Reinhard Zumkeller, Apr 02 2014
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MAPLE
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a:= n-> (s-> parse(cat(s[-i]$i=1..length(s))))(""||(2^n)):
seq(a(n), n=0..50); # Alois P. Heinz, Jan 21 2020
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MATHEMATICA
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Table[FromDigits[Reverse[IntegerDigits[2^n]]], {n, 0, 35}] (* Vincenzo Librandi, Jan 22 2020 *)
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PROG
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(Haskell)
a004094 = a004086 . a000079 -- Reinhard Zumkeller, Apr 02 2014
(PARI) rev(n)=subst(Polrev(digits(n)), 'x, 10)
a(n)=rev(2^n) \\ Charles R Greathouse IV, Oct 20 2014
(PARI) apply( {A004094(n)=fromdigits(Vecrev(digits(2^n)))}, [0..44]) \\ M. F. Hasler, Feb 18 2021
(Magma) [Seqint(Reverse(Intseq(2^n))): n in [0..35]]; // Vincenzo Librandi, Jan 22 2020
(Python)
def A004094(n):
return int(str(2**n)[::-1]) # Chai Wah Wu, Feb 19 2021
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CROSSREFS
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Cf. A014963, A102382, A102383, A102384, A102385.
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).
Cf. A004086 (read n backwards).
For indices of primes see A057708.
Sequence in context: A206850 A094333 A018473 * A028910 A018482 A036447
Adjacent sequences: A004091 A004092 A004093 * A004095 A004096 A004097
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KEYWORD
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nonn,base,easy
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AUTHOR
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N. J. A. Sloane
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EXTENSIONS
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More terms from Reinhard Zumkeller, Jan 05 2005
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STATUS
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approved
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