A111347 Numbers n such that the result of swapping the 2nd and next to the last digit of n is prime.

11, 13, 14, 16, 17, 20, 30, 31, 32, 34, 35, 37, 38, 50, 70, 71, 73, 74, 76, 79, 91, 92, 95, 97, 98, 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

Offset: 1

Author

Cino Hilliard, Nov 05 2005

Keywords

• easy
• nonn
• base

Comments

Similar to A007934 and A095179 for the first few terms.

Since these numbers are just digit permutations of the primes the sequence is obviously infinite. - Charles R Greathouse IV, Oct 20 2008

Crossrefs

Cf. A007934, A095179, A111348, A111349.

Programs

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",")) ) }

Formula

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.