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A239697 Smallest m such that m and reverse(m) each have n (not necessarily distinct) prime factors. 2
2, 4, 8, 88, 252, 2576, 8820, 2112, 4224, 8448, 44544, 48384, 846720, 4078080, 405504, 4091904, 441606144, 405909504, 886898688, 677707776, 4285005824, 63769149440, 21128282112, 633498894336, 2701312131072, 6739855589376, 29142024192, 65892155129856, 4815463645184, 445488555884544, 23088546155855872 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For all terms thus far, both m and reverse(m) are even.

a(24) > 10^11. - Giovanni Resta, Mar 31 2014

LINKS

Table of n, a(n) for n=1..31.

FORMULA

{min m: A001222(m) = A001222(A004086(m))}. - R. J. Mathar, Apr 04 2014

EXAMPLE

2576 = 2*2*2*2*23*7 (6 factors)

6752 = 2*2*2*2*2*211 (6 factors)

Since 2576 is the smallest number with this property, a(6) = 2576.

MAPLE

A239697 := proc(n)

    local a;

    for a from 1 do

        if numtheory[bigomega](a) = n then

            if numtheory[bigomega](digrev(a)) =n then

                return a;

            end if;

        end if;

    end do:

end proc: # R. J. Mathar, Apr 04 2014

PROG

(Python)

import sympy

from sympy import factorint

from sympy import primorial

def Rev(x):

..rev = ''

..for i in str(x):

....rev = i + rev

..return int(rev)

def RevFact(x):

..n = 2

..while n <= primorial(x):

....if sum(list(factorint(n).values())) == x:

......if sum(list(factorint(Rev(n)).values())) == x:

........return n

......else:

........n += 1

....else:

......n += 1

x = 1

while x < 50:

..print(RevFact(x))

..x += 1

CROSSREFS

Cf. A237912, A237913.

Sequence in context: A089337 A088114 A348050 * A237913 A076886 A309565

Adjacent sequences:  A239694 A239695 A239696 * A239698 A239699 A239700

KEYWORD

nonn,base

AUTHOR

Derek Orr, Mar 24 2014

EXTENSIONS

a(17)-a(23) from Giovanni Resta, Mar 31 2014

STATUS

approved

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Last modified September 29 01:05 EDT 2022. Contains 357082 sequences. (Running on oeis4.)