a(n) = (n*(6*n+1)+(n+2)*(-1)^n)/2.

Terms

a(0) =1a(1) =2a(2) =15a(3) =26a(4) =53a(5) =74a(6) =115a(7) =146a(8) =201a(9) =242a(10) =311a(11) =362a(12) =445a(13) =506a(14) =603a(15) =674a(16) =785a(17) =866a(18) =991a(19) =1082a(20) =1221a(21) =1322a(22) =1475a(23) =1586a(24) =1753a(25) =1874a(26) =2055a(27) =2186a(28) =2381a(29) =2522