A000318Generalized tangent numbers d(4,n).

4, 128, 16384, 4456448, 2080374784, 1483911200768, 1501108249821184, 2044143848640217088, 3605459138582973251584, 7995891855149741436305408, 21776918737280678860353961984, 71454103701490016776039304265728, 278008871543597996197497752082448384

The first 2 terms appear at position 1,863.

…4225125205117392984896084128488626945604241965285022…
position 1,863
termsstringfirst positionoccurrences
142100,011,958
241281,863100,564
3412816384not within 1,000,000,0000

Searched the first 1,000,000,000 digits. Strings longer than 12 digits are not indexed.