This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A057708 Numbers n such that 2^n reversed is prime. 9
 1, 4, 5, 7, 10, 17, 24, 37, 45, 55, 70, 77, 107, 137, 150, 271, 364, 1157, 1656, 2004, 2126, 3033, 3489, 3645, 4336, 6597, 7279, 12690, 13840, 20108, 21693, 28888, 84155, 102930 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(35) > 105000. - Giovanni Resta, Feb 22 2013 LINKS EXAMPLE 4 is a member 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 *) CROSSREFS Sequence in context: A145018 A018910 A022936 * A032686 A074300 A047375 Adjacent sequences:  A057705 A057706 A057707 * A057709 A057710 A057711 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 16 13:24 EST 2018. Contains 318167 sequences. (Running on oeis4.)