A308468 - cp's OEIS frontend

A308468 "Trapezoidal numbers": numbers k such that the integers from 1 to k can be arranged in a trapezoid of H lines containing respectively L, L-1, L-2, ..., L-H+1 numbers from top to bottom. The rule is that from the second line, each integer is equal to the absolute value of the difference between the two numbers above it.

n	a(n)
1	3
2	5
3	6
4	7
5	9
6	10
7	11
8	12
9	13
10	14
11	15
12	17
13	18
14	19
15	20
16	21
17	23
18	24
19	25
20	27
21	29
22	30
23	31
24	33
25	35
26	36
27	37
28	39
29	41
30	42
31	43
32	45
33	47
34	48
35	49
36	51
37	53

[3, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 23, 24, 25, 27, 29, 30, 31, 33, 35, 36, 37, 39, 41, 42, 43, 45, 47, 48, 49, 51, 53]