222327domain: NAppears in sequencesNumbers k such that k^2 contains only digits {2,4,9}.at n=12A053924Numbers k such that k and k^2 use only the digits 2, 3, 4, 7 and 9.at n=8A137075The Wiener index of the para-polyphenyl chain with n hexagons (see the Dou et al. and the Deng references).at n=20A216112