A102496 Values of n for which the concatenation of the form 1nn1 (sequence A100846) are primes.

12, 13, 15, 19, 27, 31, 34, 36, 40, 42, 45, 49, 57, 58, 61, 69, 70, 72, 78, 82, 87, 90, 91, 96, 97, 1000, 1002, 1017, 1018, 1024, 1033, 1035, 1063, 1068, 1069, 1074, 1084, 1086, 1090, 1095, 1110, 1114, 1116, 1117, 1126, 1128, 1173, 1174, 1179, 1185, 1189, 1192

Offset: 1

Author

Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 12 2005

Keywords

• easy
• nonn
• base

Comments

All terms == 0 or 1 (mod 3), and have an even number of decimal digits. - Robert Israel, May 09 2017

Examples

			For n=12 we have 112121, which is prime.
For n=13 we have 113131, which is prime.
For n=1000 we have 1100010001, which is prime.
		

Links

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

Crossrefs

Cf. A100846. The primes themselves are in sequence A102497.

Programs

Maple

f:= n -> 1 + 1*10^(2*ilog10(n)+3)+(n)*(10+10^(2+ilog10(n))):
select(n -> isprime(f(n)), [$1..2000]); # Robert Israel, May 09 2017

Mathematica

Select[Range@ 1200, PrimeQ[FromDigits@ Join[{1}, #, #, {1}]] &@ IntegerDigits[#] &] (* Michael De Vlieger, May 09 2017 *)