61800

Appears in sequences

• Consider sequence of fractions A066657/A066658 produced by ratios of terms in A066720; let m = smallest integer such that all fractions 1/n, 2/n, ..., (n-1)/n have appeared when we reach A066720(m) = k; sequence gives values of k; set a(n) = -1 if some fraction i/n never appears.at n=9A066848
• a(0)=1; a(n) = sigma_1(n) + sigma_3(n).at n=38A092345
• a(n) is the Wiener index of a broom on 2n vertices of which n+2 are pendant.at n=42A349416