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

Offset: 0

Author

Patrick De Geest, Feb 15 2000

Keywords

• nonn
• base

Examples

			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.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A054256, A054258.

Programs

Mathematica

Select[Range[5000],PrimeQ[FromDigits[Flatten[Table[IntegerDigits[#,n],{n,10,2,-1}]]]]&] (* Harvey P. Dale, May 25 2012 *)