A291830 Numbers k such that k^4 is sum of two positive 7th powers.

4, 512, 8748, 16641, 65536, 312500, 1119744, 2130048, 3294172, 4787344, 5359225, 8388608, 19131876, 36393867, 40000000, 77948684, 143327232, 250994068, 268468225, 272646144, 344882041, 421654016, 612780032, 683437500, 685980800, 1073741824, 1300078125

Offset: 1

Author

XU Pingya, Sep 03 2017

Keywords

• nonn

Comments

When a^7 + b^7 = m, (ma)^7 + (mb)^7 = m^8 is 4th power.

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

Examples

			4^4 = 2^7 + 2^7, so 4 is in the sequence.
16641^4 = 129^7 + 358^7, so 16641 is in the sequence.
		

Crossrefs

Cf. A000583, A001015, A000404, A009003, A050801.

Programs

Mathematica

lst={};Do[If[IntegerQ[(n^4-a^7)^(1/7)],AppendTo[lst,n]],{n,1.4*10^9},{a,(n^4/2)^(1/7)}]; lst