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

Author

Amiram Eldar, Aug 19 2017

Keywords

• nonn

Comments

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

Examples

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

Links

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

Crossrefs

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

Programs

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] &]

Extensions

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