a(n) is the least number x such that gcd(sigma(x), sigma(x+1)) = n.

Terms

a(0) =1a(1) =13a(2) =17a(3) =6a(4) =199a(5) =5a(6) =242a(7) =27a(8) =391a(9) =57a(10) =1296a(11) =22a(12) =882a(13) =12a(14) =648a(15) =93a(16) =175232a(17) =89a(18) =3872a(19) =236a(20) =195a(21) =1032a(22) =4875263a(23) =14a(24) =5739271a(25) =467a(26) =35377a(27) =83a(28) =1882384a(29) =58