Odd 9-gonal (nonagonal) pyramidal numbers.

Terms

a(0) =1a(1) =155a(2) =885a(3) =2639a(4) =5865a(5) =11011a(6) =18525a(7) =28855a(8) =42449a(9) =59755a(10) =81221a(11) =107295a(12) =138425a(13) =175059a(14) =217645a(15) =266631a(16) =322465a(17) =385595a(18) =456469a(19) =535535a(20) =623241a(21) =720035a(22) =826365a(23) =942679a(24) =1069425a(25) =1207051a(26) =1356005a(27) =1516735a(28) =1689689a(29) =1875315