A032711 Numbers k such that k prefixed by '2' and followed by '3' is prime.
2, 3, 6, 8, 9, 11, 14, 15, 20, 21, 24, 27, 29, 33, 38, 39, 42, 47, 50, 54, 59, 63, 66, 68, 69, 71, 75, 80, 83, 84, 90, 95, 96, 101, 102, 114, 116, 119, 128, 131, 132, 138, 143, 149, 150, 152, 156, 161, 167, 168, 171, 177, 180, 186, 189, 194, 200, 201, 206, 207, 209
Offset: 1
Examples
8 and 21 are in the sequence because 283 and 2213 are primes.
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
v={};Do[If[PrimeQ[FromDigits[Join[{2},IntegerDigits[n],{3}]]], v=Append[v,n]],{n, 260}];v (* Farideh Firoozbakht, Jun 15 2003 *) Select[Range[210],PrimeQ[FromDigits[Join[{2},IntegerDigits[#],{3}]]]&] (* Harvey P. Dale, May 02 2012 *) -
PARI
for( n=1,300, isprime(eval(Str(2,n,3))) & print1(n",")) \\ M. F. Hasler, Mar 18 2008
Extensions
Merged with data from duplicate entry A092114. - M. F. Hasler, Mar 18 2008
Comments