A081495 - cp's OEIS frontend

A081495 Start with Pascal's triangle; form a rhombus by sliding down n steps from top on both sides then sliding down inwards to complete the rhombus and then deleting the inner numbers; a(n) = sum of entries on perimeter of rhombus.

n	a(n)
1	1
2	5
3	17
4	55
5	189
6	681
7	2519
8	9451
9	35765
10	136153
11	520695
12	1998745
13	7696467
14	29716025
15	115000947
16	445962899
17	1732525861
18	6741529113
19	26270128535
20	102501265057
21	400411345659
22	1565841089321
23	6129331763923
24	24014172955545
25	94163002754699
26	369507926510401

[1, 5, 17, 55, 189, 681, 2519, 9451, 35765, 136153, 520695, 1998745, 7696467, 29716025, 115000947, 445962899, 1732525861, 6741529113, 26270128535, 102501265057, 400411345659, 1565841089321, 6129331763923, 24014172955545, 94163002754699, 369507926510401]

cp's OEIS Frontend

A081495 Start with Pascal's triangle; form a rhombus by sliding down n steps from top on both sides then sliding down inwards to complete the rhombus and then deleting the inner numbers; a(n) = sum of entries on perimeter of rhombus.

Table of values

List of values