A112981 a(1) = a(2) = a(3) = 1; for n>3: a(n) = a(n-1)^3 + a(n-2)^3 + a(n-3)^3.

1, 1, 1, 3, 29, 24417, 14557168544129, 3084826414596074361107793217201624802791

Offset

1,4

Comments

A cubic tribonacci sequence.

This is a cubic analog of a tribonacci sequence A000213, similarly to A000283 being the quadratic analog of the Fibonacci sequence A000045. a(4) and a(5) are primes; a(7) is semiprime; a(6) and a(8) have 3 prime factors. a(9) has 119 digits.

Links

Table of n, a(n) for n=1..8.

Example

a(6) = 1^3 + 3^3 + 29^3 = 24417.

Mathematica

RecurrenceTable[{a[1]==a[2]==a[3]==1, a[n]==a[n-1]^3+a[n-2]^3+a[n-3]^3}, a, {n, 10}] (* Harvey P. Dale, Jan 25 2018 *)

Crossrefs

Cf. A000045, A000213, A000283.

Sequence in context: A139517 A156026 A171883 * A178336 A176495 A318971

Adjacent sequences: A112978 A112979 A112980 * A112982 A112983 A112984

Keyword

easy,nonn

Author

Jonathan Vos Post, Jan 02 2006

Status

approved