A099678 Numbers n such that 10n01 is a prime.

3, 5, 6, 15, 17, 20, 21, 23, 27, 30, 38, 47, 48, 54, 56, 57, 65, 68, 71, 72, 83, 84, 90, 92, 102, 105, 110, 116, 122, 126, 134, 135, 143, 155, 156, 162, 164, 173, 182, 183, 197, 198, 200, 201, 203, 204, 210, 213, 222, 225, 227, 231, 233, 236, 249, 261, 264, 270, 281, 282, 290

Offset: 1

Author

N. J. A. Sloane, Nov 19 2004

Keywords

• nonn
• base

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A032672, A100502 (for the primes).

Programs

Maple

t0:=[]; u0:=[]; for n from 0 to 500 do p0:="10"; p1:="01"; t1:=cat(p0,n,p1); t1:=convert(t1,decimal,10); if isprime(t1) then t0:=[op(t0),n]; u0:=[op(u0),t1]; fi; od: t0;
# Alternative:
filter:= n -> isprime( 10^(ilog10(n)+4)+100*n+1):
select(filter, [$1..1000]); # Robert Israel, Mar 16 2017

Mathematica

Select[ Range[280], PrimeQ[ FromDigits[Join[{1, 0}, IntegerDigits[ # ], {0, 1}]]] &] (* Robert G. Wilson v, Nov 20 2004 *)

PARI

isok(n) = isprime(eval(concat(concat("10", n), "01"))); \\ Michel Marcus, Jul 29 2015