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Combinatorics

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Segments of DNA

COMBIN-XY51YB

A segment of DNA can be modeled as a string of symbols from the set $\{$C, G, A, T$\}$.

How many segments of length 5 are possible if two segments that can be obtained from each other by reversal are regarded as the same?

For instance, the segments GGCTA and ATCGG are the same.

A

$256$

B

$480$

C

$512$

D

$520$

E

$544$