A004094 Powers of 2 written backwards.

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

Offset

0,2

Comments

Freeman Dyson believes that A014963(a(n)) <> 5 is true but cannot be proved, see link. - Reinhard Zumkeller, Jan 05 2005

Links

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.

Formula

a(n) = A004086(A000079(n)). - Reinhard Zumkeller, Apr 02 2014

Maple

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

Mathematica

Table[FromDigits[Reverse[IntegerDigits[2^n]]], {n, 0, 35}] (* Vincenzo Librandi, Jan 22 2020 *)

Prog

(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

Crossrefs

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

Keyword

nonn,base,easy

Author

N. J. A. Sloane

Extensions

More terms from Reinhard Zumkeller, Jan 05 2005

Status

approved