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.

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.

Terms

    a(0) =1a(1) =5a(2) =17a(3) =55a(4) =189a(5) =681a(6) =2519a(7) =9451a(8) =35765a(9) =136153a(10) =520695a(11) =1998745a(12) =7696467a(13) =29716025a(14) =115000947a(15) =445962899a(16) =1732525861a(17) =6741529113a(18) =26270128535a(19) =102501265057a(20) =400411345659

External references