A048985 - OEIS

A048985

Working in base 2, replace n with the concatenation of its prime divisors in increasing order (write answer in base 10).

1, 2, 3, 10, 5, 11, 7, 42, 15, 21, 11, 43, 13, 23, 29, 170, 17, 47, 19, 85, 31, 43, 23, 171, 45, 45, 63, 87, 29, 93, 31, 682, 59, 81, 47, 175, 37, 83, 61, 341, 41, 95, 43, 171, 125, 87, 47, 683, 63, 173, 113, 173, 53, 191, 91, 343, 115, 93, 59, 349, 61, 95, 127, 2730

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Patrick De Geest, Home Primes

EXAMPLE

15 = 3*5 -> 11.101 -> 11101 = 29, so a(15) = 29.

MATHEMATICA

f[n_] := FromDigits[ Flatten[ IntegerDigits[ Flatten[ Table[ #1, {#2}] & @@@ FactorInteger@n], 2]], 2]; Array[f, 64] (* Robert G. Wilson v, Jun 02 2010 *)

PROG

(Haskell)

-- import Data.List (unfoldr)

a048985 = foldr (\d v -> 2 * v + d) 0 . concatMap

(unfoldr (\x -> if x == 0 then Nothing else Just $ swap $ divMod x 2))

. reverse . a027746_row

-- Reinhard Zumkeller, Jul 16 2012

(Python)

from sympy import factorint

def a(n):

if n == 1: return 1

return int("".join(bin(p)[2:]*e for p, e in factorint(n).items()), 2)