A291829 Numbers k such that k^3 is the sum of two positive 7th powers.

32, 4096, 69984, 524288, 2500000, 8957952, 26353376, 67108864, 153055008, 320000000, 623589472, 1146617856, 2007952544, 3373232128, 5467500000, 8589934592, 13130837536, 19591041024, 28603895648, 35723051649, 40960000000, 57634833312, 79819452416, 108954414304

Offset

1,1

Comments

When a^7 + b^7 = m, (m^2*a)^7 + (m^2*b)^7 = m^15 is a cube.

When k in this sequence, k*(n^7) (n = 2, 3, ... ) is also in this sequence.

Links

Table of n, a(n) for n=1..24.

Example

32^3 = 4^7 + 4^7, so 32 is in the sequence.
35723051649^3 = 16641^7 + 33282^7, so 35723051649 is in the sequence.

Mathematica

lst={}; Do[If[IntegerQ[(n^3-a^7)^(1/7)], AppendTo[lst, n]], {n, 1.467*10^11}, {a, (n^3/2)^(1/7)}]; lst

Crossrefs

Cf. A000578, A001015, A000404, A009003, A050801.

Sequence in context: A264126 A304401 A328275 * A248075 A248000 A278302

Adjacent sequences: A291826 A291827 A291828 * A291830 A291831 A291832

Keyword

nonn

Author

XU Pingya, Sep 03 2017

Status

approved