Define the ECHO sequence {bn} recursively by (b 0 , b 1 , b 2 , b 3 ) = (1, 1, 2, 1) and for n ≥ 4,We relate this sequence {bn} to the coordinates of points on the elliptic curve E : y 2 + y = x 3 − 3x + 4. We use Galois representations attached to E to prove that the density of primes dividing a term in this sequence is equal to 179 336 . Furthermore, we describe an infinite family of elliptic curves whose Galois images match those of E.

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