A032609 Concatenation of n and n + 4 or {n,n+4}.
15, 26, 37, 48, 59, 610, 711, 812, 913, 1014, 1115, 1216, 1317, 1418, 1519, 1620, 1721, 1822, 1923, 2024, 2125, 2226, 2327, 2428, 2529, 2630, 2731, 2832, 2933, 3034, 3135, 3236, 3337, 3438, 3539, 3640, 3741, 3842, 3943, 4044, 4145, 4246
Offset: 1