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 A102496 Values of n for which the concatenation of the form 1nn1 (sequence A100846) are primes. 3
 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified July 21 18:17 EDT 2024. Contains 374475 sequences. (Running on oeis4.)