A061806 Numbers n such that the iterative cycle: n -> sum of digits of n^2 has only three distinct elements.
4, 5, 17, 26, 28, 32, 37, 40, 43, 44, 49, 50, 53, 62, 63, 64, 67, 73, 74, 76, 77, 82, 83, 86, 87, 88, 89, 91, 92, 93, 94, 97, 98, 107, 109, 113, 114, 116, 117, 118, 122, 124, 125, 126, 127, 128, 133, 137, 141, 143, 149, 154, 157, 158, 161, 164, 166, 167, 169, 170
Offset: 1
Examples
4 -> 1+6 = 7 -> 4+9 = 13 -> 1+6+9 = 16 -> 2+5+6 = 13, thus {7,13,16} are the only distinct elements of the iterative cycle of 4.