1,1

These are semiprimes when read as base 3 numbers and their reversals are different semiprimes when read as base 3 numbers. Base 10 these are: 14, 22, 34, 38, 46, 58, 62, 74, 94, 118, 122, 146, 155, 158, 178, 185, 187, ... See: A097393 Emirpimes: numbers n such that n and its reversal are distinct semiprimes. See: A004086 Read n backwards (referred to as R(n) in many sequences). See: A007089 Numbers in base 3.

Eric Weisstein, Jonathan Vos Post, et al., Emirpimes.

Eric Weisstein, Vincenzo Origlio, et al., Ternary.

a(n) = A007089(i) for some i in A001358 and R(a(n)) = A007089(j) for some j =/= i in A001358. a(n) = A007089(i) for some i in A001358 and A004086(a(n)) = A007089(j) for some j =/= i in A001358.

a(1) = 112 because 112 (base 3) = 14 (base 10) is semiprime and R(112) = 211, where 211 (base 3) = 22 (base 10) is a different semiprime.

a(13) = 12202 because 12202 (base 3) = 155 (base 10) is semiprime and R(12202) = 20221, where 20221 (base 3) = 187 (base 10) is a different semiprime.

Cf. A001358, A004086, A007089, A097393.

Sequence in context: A157662 A095615 A061281 this_sequence A119742 A154063 A047631

Adjacent sequences: A119681 A119682 A119683 this_sequence A119685 A119686 A119687

base,easy,nonn

Jonathan Vos Post (jvospost3(AT)gmail.com), Jun 08 2006