A058997 Least power k greater than 1 for which n^k reversed is a prime, or 0 if impossible.

0, 4, 0, 2, 3, 0, 12, 8, 0, 0, 0, 0, 379, 2, 0, 6, 11, 0, 2, 0, 0, 0, 8, 0, 13, 47, 0, 2, 7, 0, 4, 2, 0, 1731, 4, 0, 2, 2, 0, 0, 2, 0, 5, 0, 0, 22, 15, 0, 6, 0, 0, 3, 10, 0, 0, 143, 0, 88, 12, 0, 4, 2, 0, 4, 8, 0, 39, 83, 0, 0, 7, 0, 11, 38, 0, 7, 0, 0, 4, 0, 0, 6, 11, 0, 2, 28, 0, 0, 2, 0, 18, 55, 0

Offset

1,2

Links

Robert Israel, Table of n, a(n) for n = 1..230

Maple

rev:= proc(n) local L, i;
  L:= convert(n, base, 10);
  add(L[-i]*10^(i-1), i=1..nops(L))
end proc:
f:= proc(n) local k;
   if n mod 10 = 0 or n mod 11 = 0 or n mod 3 = 0 then return 0 fi;
   for k from 2 to 10000 do if isprime(rev(n^k)) then return k fi od;
   FAIL
end proc:
f(1):= 0:
map(f, [$1..100]); # Robert Israel, Dec 22 2024

Mathematica

Do[ If[ Mod[ n, 3 ] != 0 && Mod[ n, 10 ] != 0 && Mod[ n, 11 ] != 0, k = 2; While[ !PrimeQ[ ToExpression[ StringReverse[ ToString[ n^k ] ] ] ], k++ ]; Print[ k ], Print[ 0 ] ], {n, 2, 33} ]

Crossrefs

Sequence in context: A109157 A226955 A123314 * A261164 A323982 A279415

Adjacent sequences: A058994 A058995 A058996 * A058998 A058999 A059000

Keyword

base,nonn

Author

Robert G. Wilson v, Jan 17 2001

Extensions

More terms from Robert Israel, Dec 22 2024

Status

approved