1,1

These are semiprimes when read as base 4 numbers, and their reversals are different semiprimes when read as base 4 numbers. Base 4 analogue of what for base 3 is A119684 and for base 10 is A097393. The base 10 representation of this sequence is: 6, 9, 74, 87, 106, 111, 115, 119, 123, 133, 134, 142, 146, 161, 169, 178, 205, 213, 221, 237.

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

Eric Weisstein's World of Mathematics, Quaternary.

a(n) = A007090(i) for some i in A001358, and R(a(n)) = A007090(j) for some j =/= i in A001358. a(n) = A007090(i) for some i in A001358, and A004086(a(n)) = A007090(j) for some j =/= i in A001358.

a(1) = 12 because 12 (base 4) = 6 (base 10) is semiprime, and R(12) = 21, where 21 (base 4) = 9 (base 10) is a different semiprime.

a(19) = 3131 because 3131 (base 4) = 221 (base 10) = 13 * 17 (base 10) is semiprime, and R(3131) = 1313, where 1313 (base 4) = 119 (base 10) = 7 * 17 (base 10) is a different semiprime.

Cf. A001358, A004086, A007090, A097393.

Adjacent sequences: A114012 A114013 A114014 this_sequence A114016 A114017 A114018

Sequence in context: A134514 A030299 A001292 this_sequence A065439 A031186 A078538

base,easy,nonn,less

Jonathan Vos Post (jvospost2(AT)yahoo.com), Jun 13 2006