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A111337 Primes with at least two digits such that swapping the second and the penultimate digit yields a prime. 1
11, 13, 17, 31, 37, 71, 73, 79, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Is this sequence infinite?
LINKS
EXAMPLE
The prime 612041 is in the sequence because swapping the second and the penultimate digit yields 642011, which is prime.
MATHEMATICA
a = {}; For[n = 5, n < 100, n++, b = IntegerDigits[Prime[n]]; {b[[2]], b[[ -2]]} = {b[[ -2]], b[[2]]}; If[PrimeQ[FromDigits[b]], AppendTo[a, Prime[n]]]]; a
PROG
(PARI) swap(n, d) = \ d is the digit position to swap { local(j, ln, x, s, y, y2, tmp); forprime(x=10^(d-1), 10^(d-1)+n, s = Str(x); ln = length(s); y = eval(Vec(s)); tmp=y[d]; y[d]=y[ln-d+1]; y[ln-d+1]=tmp; y2=0; for(j=1, ln, y2+=y[j]*10^(ln-j); ); if(isprime(y2), print1(x", ")) ) }
CROSSREFS
Sequence in context: A166009 A240107 A105892 * A359136 A359137 A266675
KEYWORD
base,easy,nonn
AUTHOR
Cino Hilliard, Nov 05 2005
EXTENSIONS
Edited by Stefan Steinerberger, Aug 01 2007
STATUS
approved

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Last modified March 28 14:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)