A036447 Double and reverse digits.

1, 2, 4, 8, 61, 221, 244, 884, 8671, 24371, 24784, 86594, 881371, 2472671, 2435494, 8890784, 86518771, 245730371, 247064194, 883821494, 8892467671, 24353948771, 24579870784, 86514795194, 883095920371, 2470481916671, 2433383690494

Offset: 0

Author

Rodolfo Kurchan

Keywords

• nonn
• base
• easy
• nice

Links

• Harvey P. Dale, Table of n, a(n) for n = 0..1000
• Nick Hobson, Python program for this sequence

Crossrefs

Cf. A004086, A004093.

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. A132064, A045539, A132078, A132114, A132113, A133361.

Programs

Haskell

a036447 n = a036447_list !! n
a036447_list = iterate a004093 1  -- Reinhard Zumkeller, Feb 09 2012

Mathematica

NestList[ FromDigits[ Reverse[ IntegerDigits[ 2# ] ] ] &, 1, 27 ]
NestList[IntegerReverse[2#]&,1,30] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 18 2017 *)

Formula

a(n+1) = A004093(a(n)). - Reinhard Zumkeller, Feb 09 2012

Conjecture: a(n)^(1/n) tends to sqrt(10). - Vaclav Kotesovec, Jan 03 2020

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), Mar 31 2000