a(n) = (1/(2n)) * Sum_{d|n} phi(d) * 2^(2n/d) + (2^((n-4)/2), if n is even).
A058880
a(n) = (1/(2n)) * Sum_{d|n} phi(d) * 2^(2n/d) + (2^((n-4)/2), if n is even).
Terms
- a(0) =12a(1) =36a(2) =104a(3) =352a(4) =1172a(5) =4119a(6) =14572a(7) =52492a(8) =190652a(9) =699266a(10) =2581112a(11) =9587602a(12) =35791472a(13) =134219859a(14) =505290272a(15) =1908881998a(16) =7233629132a(17) =27487817244a(18) =104715393912a(19) =399822505942
External references
- oeis: A058880