A291126 Psibonacci numbers: solutions n of the equation psi(n) = psi(n-1) + psi(n-2), where psi is the Dedekind psi function (A001615).

3, 6, 210, 88200, 101970, 193290, 289680, 993990, 11264550, 59068230, 72776970, 98746230, 122460690, 126500910, 132766770, 234150930, 514442214, 531391650, 638082390, 650428020, 790769790, 1249160790, 3727074450, 4775972850, 8299675650, 9530202210

Offset

1,1

Comments

Analogous to phibonacci numbers (A065557) and other sequences (see crossrefs).

Links

Giovanni Resta, Table of n, a(n) for n = 1..70 (terms < 4*10^12)

Example

psi(210) = 576 = 240 + 336 = psi(209) + psi(208), therefore 210 is in the sequence.

Mathematica

psi[n_]:=If[n < 1, 0, n Sum[ MoebiusMu[ d]^2 / d, {d, Divisors @ n}]];
Select[Range[10^6], psi[#]==psi[#-1]+psi[#-2] &]

Crossrefs

Cf. A001615, A065557, A065900, A076136, A076251, A145469.

Sequence in context: A291982 A309258 A163423 * A083149 A348361 A290368

Adjacent sequences: A291123 A291124 A291125 * A291127 A291128 A291129

Keyword

nonn

Author

Amiram Eldar, Aug 19 2017

Extensions

a(21)-a(26) from Giovanni Resta, Aug 26 2018

Status

approved