A179826 - OEIS

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

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OFFSET

1,1

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]

LINKS

Table of n, a(n) for n=1..60.

EXAMPLE

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.

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 *)

CROSSREFS

Sequence in context: A222577 A116322 A153681 * A067832 A126242 A178057

Adjacent sequences: A179823 A179824 A179825 * A179827 A179828 A179829

KEYWORD

base,nonn

AUTHOR

Parthasarathy Nambi, Jul 29 2010

EXTENSIONS

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

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

STATUS

approved