A128972 - OEIS

A128972

n^3 - 1 divided by its largest cube divisor.

7, 26, 63, 124, 215, 342, 511, 91, 37, 1330, 1727, 2196, 2743, 3374, 4095, 614, 17, 254, 7999, 9260, 10647, 12166, 13823, 1953, 17575, 19682, 813, 24388, 26999, 29790, 32767, 4492, 39303, 42874, 46655, 1876, 54871, 59318, 63999, 8615, 74087, 79506

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OFFSET

2,1

COMMENTS

In other words, cubefree part of n^3-1, or cubefree kernel of n^3-1. Cube analog of A068310.

LINKS

Robert Israel, Table of n, a(n) for n = 2..10000

FORMULA

a(n) = A062378(A068601(n)) = A062378(n^3-1).

EXAMPLE

a(9) = (9^3-1)/8 = (2^3 * 7 * 13)/(2^3) = 728/8 = 91.

a(10) = (10^3-1)/27 = (3^3 * 37)/(3^3) = 999/27 = 37.

a(18) = (18^3-1)/343 = (7^3 * 17)/(7^3) = 5831/343 = 17.

MAPLE

a:= n -> mul(f[1]^(f[2] mod 3), f = ifactors(n^3-1)[2]):

seq(a(n), n=2..100); # Robert Israel, Sep 24 2014

CROSSREFS

Cf. A002350, A004709, A007948, A062378, A067872, A033314, A068310.

Sequence in context: A211645 A171340 A046433 * A135300 A024001 A068601

Adjacent sequences: A128969 A128970 A128971 * A128973 A128974 A128975

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Apr 28 2007

EXTENSIONS

More terms from Carl R. White, Nov 09 2010

STATUS

approved