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A090265 Numbers n such that the strings n9n and 9n9 are both prime. 4
1, 19, 41, 43, 47, 61, 67, 71, 73, 83, 107, 149, 211, 217, 221, 269, 277, 319, 437, 443, 523, 547, 553, 607, 619, 647, 679, 697, 817, 863, 877, 899, 1171, 1283, 1297, 1379, 1481, 1547, 1621, 1853, 1867, 1967, 1993, 1997, 2021, 2053, 2107, 2357, 2359, 2393 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

41 is a member as 41941 and 9419 are both prime.

MATHEMATICA

n9Q[n_]:=Module[{idn=IntegerDigits[n]}, AllTrue[{FromDigits[Join[idn, {9}, idn]], FromDigits[ Join[{9}, idn, {9}]]}, PrimeQ]]; Select[Range[2500], n9Q] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Feb 01 2016 *)

CROSSREFS

Cf. A090262, A090263, A090264.

Sequence in context: A128677 A065349 A085778 * A049485 A019393 A179849

Adjacent sequences:  A090262 A090263 A090264 * A090266 A090267 A090268

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Nov 28 2003

EXTENSIONS

More terms from mohammed bouayoun (bouyao(AT)wanadoo.fr), Feb 02 2004

STATUS

approved

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Last modified April 25 00:32 EDT 2017. Contains 285346 sequences.