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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A056728 Palindromic primes using only two distinct digits and only the exterior digit is different. 2
101, 131, 151, 181, 191, 313, 353, 373, 383, 727, 757, 787, 797, 919, 929, 13331, 15551, 16661, 19991, 72227, 75557, 76667, 78887, 79997, 1333331, 1444441, 1777771, 3222223, 3444443, 7666667, 9222229, 9888889 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Primes of the form a*(10^c + 1) + b*(10^c - 10)/9 for 1<=a<=9, 0<=b<=9, c >= 2, a <> b. - Robert Israel, Nov 02 2014

LINKS

Robert Israel, Table of n, a(n) for n = 1..127

Patrick De Geest, PDP Reference Table.

Makoto Kamada, Plateau and depression numbers of the form ABB...BBA.

MAPLE

f:= (a, b, n) -> a*(10^n + 1) + b*(10^n - 10)/9:

select(isprime, [seq(seq(seq(f(a, b, n), b={$0..9} minus {a}), a=1..9), n=2..8)]);

# Robert Israel, Nov 02 2014

MATHEMATICA

Select[Union[Flatten[Table[FromDigits[Join[{a}, PadRight[{}, n, b], {a}]], {n, 1, 7, 2}, {b, 0, 9}, {a, {1, 3, 7, 9}}]]], PrimeQ] (* Harvey P. Dale, Mar 07 2015 *)

CROSSREFS

Sequence in context: A056730 A077798 A089360 * A085112 A059758 A158089

Adjacent sequences:  A056725 A056726 A056727 * A056729 A056730 A056731

KEYWORD

nonn,base

AUTHOR

Robert G. Wilson v, Aug 11 2000

EXTENSIONS

Links added by Patrick De Geest, Nov 02 2014

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy .

Last modified July 20 11:55 EDT 2018. Contains 312804 sequences. (Running on oeis4.)