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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
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
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
Sequence in context: A089337 A088114 A348050 * A237913 A076886 A309565
KEYWORD
nonn,base
AUTHOR
Derek Orr, Mar 24 2014
EXTENSIONS
a(17)-a(23) from Giovanni Resta, Mar 31 2014
a(24)-a(31) from David A. Corneth, Oct 03 2020
STATUS
approved