A065225 Fill a triangular array by rows by writing numbers 1 up to b(0), 1 up to b(1), etc., where b(n) are the 9-gonal (nonagonal) numbers. The final elements of the rows form a(n).
1, 2, 5, 9, 5, 11, 18, 2, 11, 21, 32, 44, 11, 25, 40, 56, 73, 16, 35, 55, 76, 98, 10, 34, 59, 85, 112, 140, 15, 45, 76, 108, 141, 175, 6, 42, 79, 117, 156, 196, 237, 18, 61, 105, 150, 196, 243, 291, 15, 65, 116, 168, 221, 275, 330, 386, 47, 105, 164, 224, 285, 347, 410
Offset: 0