A118623 a(0) = 1, a(n+1) = a(n)^2 + number of divisors of a(n).

1, 2, 6, 40, 1608, 2585680, 6685741062420, 44699133553728910336256592, 1998012540454093724746522398047564450017935663454544

Offset

0,2

Links

Table of n, a(n) for n=0..8.

Index entries for sequences of form a(n+1)=a(n)^2 + ...

Formula

a(n) = A000290(a(n-1)) + A000005(a(n-1)).

Mathematica

NestList[#^2+DivisorSigma[0, #]&, 1, 10] (* Harvey P. Dale, Nov 18 2022 *)

Crossrefs

Cf. A007018.

Sequence in context: A337699 A370615 A051185 * A000612 A319633 A367365

Adjacent sequences: A118620 A118621 A118622 * A118624 A118625 A118626

Keyword

nonn

Author

Reinhard Zumkeller, May 09 2006

Status

approved