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

1,1

Comments

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

Links

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

Example

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.

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 *)

Crossrefs

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

Sequence in context: A076085 A039790 A242912 * A267615 A323032 A003894

Adjacent sequences: A102493 A102494 A102495 * A102497 A102498 A102499

Keyword

easy,nonn,base

Author

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

Status

approved