login
This site is supported by donations to The OEIS Foundation.

 

Logo

Invitation: celebrating 50 years of OEIS, 250000 sequences, and Sloane's 75th, there will be a conference at DIMACS, Rutgers, Oct 9-10 2014.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A179826 Primes that can be obtained from composite numbers by interchanging the first and last digits. 2
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 (list; graph; refs; listen; history; text; internal format)
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. [From 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] [from 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified September 17 19:32 EDT 2014. Contains 246868 sequences.