OFFSET
1,2
COMMENTS
a(35) > 105000. - Giovanni Resta, Feb 22 2013
From Bernard Schott, Jan 30 2022: (Start)
If m is an even term, then u = m/2 is a term of A350441, this because 2^m = 4^(m/2). In fact, terms of A350441 are half the even terms of this sequence here.
If m is a term multiple of 3, then k = m/3 is a term of A350442, this because 2^m = 8^(m/3). First examples: m = 24, 45, 150, 1656, ... and corresponding k = 8, 15, 50, 552, ... (End)
EXAMPLE
4 is a term because 2^4 reversed is 61 and prime.
MAPLE
with(numtheory): myarray := []: for n from 1 to 4000 do it1 := convert(2^n, base, 10): it2 := sum(10^(nops(it1)-i)*it1[i], i=1..nops(it1)): if isprime(it2) then printf(`%d, `, n) fi: od:
MATHEMATICA
Do[ If[ PrimeQ[ FromDigits[ Reverse[ IntegerDigits[2^n]] ]], Print[ n]], {n, 20000}] (* Robert G. Wilson v, Jan 29 2005 *)
Select[Range[4400], PrimeQ[IntegerReverse[2^#]]&] (* Requires Mathematica version 10 or later *) (* The program generates the first 25 terms of the sequence; to generate more, increase the Range constant, but the program will take longer to run. *) (* Harvey P. Dale, Aug 05 2020 *)
PROG
(Python)
from sympy import isprime
k, m, A057708_list = 1, 2, []
while k <= 10**3:
if isprime(int(str(m)[::-1])):
A057708_list.append(k)
k += 1
m *= 2 # Chai Wah Wu, Mar 09 2021
(PARI) isok(m) = isprime(fromdigits(Vecrev(digits(2^m)))) \\ Mohammed Yaseen, Jul 20 2022
CROSSREFS
KEYWORD
base,nonn,more
AUTHOR
G. L. Honaker, Jr., Oct 23 2000
EXTENSIONS
More terms from Chris Nash (chris_nash(AT)prodigy.net), Oct 25 2000
Two more terms from Robert G. Wilson v, Jan 29 2001
3 more terms from Farideh Firoozbakht, Aug 05 2004
a(33)-a(34) from Giovanni Resta, Feb 22 2013
STATUS
approved