A179826 Primes that can be obtained from composite numbers by interchanging the first and last digits.

41, 61, 2, 3, 23, 43, 53, 83, 5, 7, 47, 67, 19, 29, 59, 89, 401, 601, 11, 211, 811, 911, 421, 521, 821, 31, 331, 431, 631, 41, 241, 541, 641, 251, 61, 461, 661, 71, 271, 571, 281, 881, 491, 691, 2, 3, 103, 503, 13, 613, 23, 223, 523, 823, 233, 433, 43, 443, 643, 53

Offset: 1

Author

Parthasarathy Nambi, Jul 29 2010

Keywords

• base
• nonn

Comments

The composite number must contain at least two digits.

Primes may be repeated; the reverted A002808(j) are investigated along increasing j and their trailing zeros become leading zeros and are dropped. [R. J. Mathar, Jul 30 2010]

Examples

			41 is a prime from the composite number 14 by interchanging the first and last digit. 47 is a prime from the composite number 74 by interchanging the first and last digit.
		

Programs

Mathematica

nonpr=Complement[Range[10,1000],Prime[Range[PrimePi[1000]]]];
swtch[n_]:=Module[{idn=IntegerDigits[n],f,l,m},f=First[idn];l=Last[idn];m=Most[Rest[idn]];FromDigits[Join[{l},m,{f}]]]
Select[swtch[#]&/@nonpr,PrimeQ] (* Harvey P. Dale, Dec 14 2010 *)

Extensions

Minor edits by N. J. A. Sloane, Jul 29 2010

More terms from R. J. Mathar, Jul 30 2010