A069706 - OEIS

%I #13 Nov 12 2015 01:58:13

%S 2,3,5,7,11,13,17,31,37,71,73,79,97,101,107,113,131,149,151,157,167,

%T 179,181,191,199,311,313,337,347,353,359,373,383,389,701,709,727,733,

%U 739,743,751,757,761,769,787,797,907,919,929,937,941,953,967,971,983,991,1009,1013

%N Primes with property that swapping first and last digits also gives a prime.

%C This is not the same as A007500, "palindromic" primes.

%H Chai Wah Wu, <a href="/A069706/b069706.txt">Table of n, a(n) for n = 1..10000</a>

%e 1049 and 9041 both are primes hence both are members.

%p swapdigs:= proc(n) local d;

%p   d:= ilog10(n);

%p   n + ((n mod 10)-floor(n/10^d))*(10^d-1);

%p end proc:

%p select(isprime and isprime @ swapdigs, [2,seq(2*i+1,i=1..10^4)]); # _Robert Israel_, Nov 11 2015

%t Do[t = IntegerDigits[ Prime[n]]; u = t; u[[1]] = t[[ -1]]; u[[ -1]] = t[[1]]; t = FromDigits[u]; If[ PrimeQ[t], Print[ Prime[n]]], {n, 1, 300}]

%o (Python)

%o from sympy import prime, isprime

%o A069706_list = [2,3,5,7]

%o for i in range(5,10**6):

%o     p = prime(i)

%o     s = str(p)

%o     if isprime(int(s[-1]+s[1:-1]+s[0])):

%o         A069706_list.append(p) # _Chai Wah Wu_, Nov 11 2015

%Y Cf. A007500, A069707, A069708.

%K nonn,base

%O 1,1

%A _Amarnath Murthy_, Apr 08 2002

%E Edited and extended by _Robert G. Wilson v_, Apr 12 2002

%E Edited by _N. J. A. Sloane_, Jan 20 2009