a(0) = 1; a(n) = Sum_{k=1..n} (-1)^(k+1)*sigma_2(k+1)*a(n-k), where sigma_2() is the sum of squares of divisors (A001157).
A307242
a(0) = 1; a(n) = Sum_{k=1..n} (-1)^(k+1)*sigma_2(k+1)*a(n-k), where sigma_2() is the sum of squares of divisors (A001157).
Terms
- a(0) =1a(1) =5a(2) =15a(3) =46a(4) =159a(5) =570a(6) =2036a(7) =7208a(8) =25400a(9) =89456a(10) =315335a(11) =1112286a(12) =3923867a(13) =13841052a(14) =48818892a(15) =172186234a(16) =607314043a(17) =2142064478a(18) =7555322206a(19) =26648517536a(20) =93992371863a(21) =331521717928
External references
- oeis: A307242