A054257 - OEIS

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A054257

Concatenation of n in base 10 down up to base 2 is prime, all numbers are interpreted as decimals.

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

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: A306532 A219154 A372292 * A341570 A297316 A079417

Adjacent sequences: A054254 A054255 A054256 * A054258 A054259 A054260

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, Feb 15 2000

STATUS

approved