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A234348
Numbers k such that both distances from k to two nearest cubes are perfect cubes.
2
0, 1, 152, 189, 513, 728, 5859, 6832, 64008, 68913, 150605, 155736, 345744, 355167, 1062936, 1090999, 1481571, 1520848, 6653933, 6742008, 7665056, 7742709, 9667693, 9796248, 15253056, 15438185, 16582104, 16592023, 16766568, 16776487, 26201448, 26460217, 28672299
OFFSET
1,3
COMMENTS
Except a(1)=0, a(n) are numbers k such that both k-x and y-k are perfect cubes, where x and y are two nearest to k cubes: x < k <= y.
LINKS
EXAMPLE
152 is in the sequence because the following are cubes: 152-125=27 and 216-152=64, where 125 and 216 are the nearest to 152 cubes.
PROG
(C)
#include <stdio.h>
#include <gmp.h> // gcc -O3 A234348.c -lgmp
int main() {
long long in=0;
mpz_t n, r, i;
mpz_init(r);
mpz_init(i);
mpz_init_set_ui(n, in);
while (in < (1ULL<<32)) {
if (mpz_root(r, n, 3) && in) mpz_sub_ui(r, r, 1);
mpz_mul(i, r, r);
mpz_mul(i, i, r);
mpz_sub(i, n, i);
if (mpz_root(i, i, 3)) {
mpz_add_ui(r, r, 1);
mpz_mul(i, r, r);
mpz_mul(i, i, r);
mpz_sub(i, i, n);
if (mpz_root(i, i, 3)) printf("%llu, ", in);
}
mpz_add_ui(n, n, 1);
if ((++in&0xfffff)==0) printf(".");
}
return 0;
}
CROSSREFS
Sequence in context: A200934 A174759 A289821 * A185394 A097640 A253367
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Dec 24 2013
STATUS
approved