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A291126
Psibonacci numbers: solutions n of the equation psi(n) = psi(n-1) + psi(n-2), where psi is the Dedekind psi function (A001615).
7
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
KEYWORD
nonn
AUTHOR
Amiram Eldar, Aug 19 2017
EXTENSIONS
a(21)-a(26) from Giovanni Resta, Aug 26 2018
STATUS
approved