A111347 - OEIS

%I #8 Nov 18 2014 12:54:15

%S 11,13,14,16,17,20,30,31,32,34,35,37,38,50,70,71,73,74,76,79,91,92,95,

%T 97,98,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,

%U 179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271

%N Numbers n such that the result of swapping the 2nd and next to the last digit of n is prime.

%C Similar to A007934 and A095179 for the first few terms.

%C Since these numbers are just digit permutations of the primes the sequence is obviously infinite. - _Charles R Greathouse IV_, Oct 20 2008

%F For N1 = a(n)*10^n + a(n-1)*10^(n-1) + ... + a(1)*10 + a(0), N2 = a(n)*10^n + a(1)*10^(n-1) + ... + a(n-1)*10 + a(0) is prime.

%o (PARI) swapn(n,d) = \ d is the digit position to swap { local(j,ln,x,s,y,y2,tmp); for(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",")) ) }

%Y Cf. A007934, A095179, A111348, A111349.

%K easy,nonn,base

%O 1,1

%A _Cino Hilliard_, Nov 05 2005