A319052 Numbers that are not the sum of {2 squares, a nonnegative cube, and a nonnegative k-th power with k >= 17}.

23, 71, 120, 312, 455, 2136, 99295

Offset

1,1

Comments

Subsequence of A022552.

Except for the above 7 terms, the remaining 427 numbers in A022552 can be expressed as the sum of two squares, a nonnegative cube and a nonnegative k-th power. So a(n) has only 7 terms, until n = 10^10.

Also, for n <= 6*10^7, when k = 3, the number of such forms is only 23; when 4 <= k <= 5, only 23 and 71; when k = 6, only 23, 71 and 455; when 7 <= k <= 8, only 23, 71 and 120; when 9 <= k <= 11, only 23, 71, 120, 312 and 455; when 12 <= k <= 16, only 23, 71, 120, 312, 455 and 2136.

Links

Table of n, a(n) for n=1..7.

W. Jagy and I. Kaplansky, Sums of Squares, Cubes and Higher Powers, Experimental Mathematics, vol. 4 (1995), pp. 169-173.

Mathematica

n=100000;
t=Union@Flatten@Table[x^2+y^2+z^3+w^17, {x, 0, n^(1/2)}, {y, x, (n-x^2)^(1/2)}, {z, 0, (n-x^2-y^2)^(1/3)}, {w, 0, (n-x^2-y^2-z^3)^(1/17)}];
Complement[Range[0, n], t]

Crossrefs

Cf. A022552, A297930.

Sequence in context: A274675 A188831 A183012 * A154619 A142405 A139962

Adjacent sequences: A319049 A319050 A319051 * A319053 A319054 A319055

Keyword

nonn,more

Author

XU Pingya, Sep 08 2018

Status

approved