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 A054257 Concatenation of n in base 10 down up to base 2 is prime, all numbers are interpreted as decimals. 4
 21, 117, 241, 283, 389, 517, 547, 627, 1219, 1223, 1247, 1285, 1287, 1323, 1467, 1505, 1591, 1599, 1689, 1713, 1817, 1961, 2203, 2309, 2377, 2607, 2837, 2847, 2899, 2911, 3227, 3261, 3499, 3823, 4007, 4069, 4183, 4347, 4403, 4473, 4507, 4535, 4637 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 EXAMPLE E.g. a(1)=21 -> 21{10}=23{9}=25{8}=30{7}=33{6}=41{5}=111{4}=210{3}=10101{2} -> 21232530334111121010101 is a prime. MATHEMATICA Select[Range[5000], PrimeQ[FromDigits[Flatten[Table[IntegerDigits[#, n], {n, 10, 2, -1}]]]]&] (* Harvey P. Dale, May 25 2012 *) CROSSREFS Cf. A054256, A054258. Sequence in context: A158091 A121628 A219154 * A297316 A079417 A267877 Adjacent sequences:  A054254 A054255 A054256 * A054258 A054259 A054260 KEYWORD nonn,base AUTHOR Patrick De Geest, Feb 15 2000. STATUS approved

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Last modified December 13 10:38 EST 2018. Contains 318086 sequences. (Running on oeis4.)