A030669 -id:A030669 - cp's OEIS frontend

A030668 Smallest nontrivial extension of n which is a cube.

125, 27, 343, 4096, 512, 64, 729, 8000, 9261, 1000, 110592, 125, 1331, 140608, 15625, 166375, 1728, 185193, 19683, 205379, 216, 226981, 238328, 24389, 250047, 262144, 2744, 287496, 29791, 300763, 314432, 32768, 3375, 343, 35937

Offset: 1

Patrick De Geest

Chai Wah Wu, Table of n, a(n) for n = 1..10000

Cf. A030669.

from gmpy2 import iroot
def A030668(n):
    d, nd = 10, 10*n
    while True:
        x = (iroot(nd-1,3)[0]+1)**3
        if x < nd+d:
            return int(x)
        d *= 10
        nd *= 10 # Chai Wah Wu, May 24 2016

A030679 Cube root of A030678.

Original entry on oeis.org

5, 3, 7, 16, 8, 4, 9, 20, 21, 48, 61, 15, 164, 82, 188, 92, 96, 215, 466, 481, 23, 236, 242, 533, 253, 258, 122, 576, 587, 277, 606, 615, 624, 632, 64, 301, 656, 143, 312, 679, 1479, 322, 70, 707, 714, 72, 1565, 34, 1593, 346, 1619, 1632, 763, 357, 1668

Offset: 1

Patrick De Geest

Robert Israel, Table of n, a(n) for n = 1..10000

Cf. A002113, A030669, A030678.

N:= 3: # to get extensions of all palindromes of <= N digits
f:= proc(n) local d, x;
  for d from 1 do
    x:= ceil((n*10^d)^(1/3));
    if x^3 < (n+1)*10^d then return x fi
  od
end proc:
digrev:= proc(n) local i, L;
  L:= convert(n, base, 10);
  add(L[-i]*10^(i-1), i=1..nops(L))
end proc:
Res:= seq(f(i), i=1..9):
for d from 2 to N do
if d::even then
    m:= d/2;
    Res:= Res, seq(f(n*10^m + digrev(n)), n=10^(m-1)..10^m-1);
else
    m:= (d-1)/2;
    Res:= Res, seq(seq(f(n*10^(m+1)+y*10^m+digrev(n)), y=0..9), n=10^(m-1)..10^m-1)
fi
od: Res; # Robert Israel, Dec 25 2018

a(n) = A030669(A002113(n+1)) = A030678(n)^(1/3). - Robert Israel, Dec 25 2018

cp's OEIS Frontend

A030668 Smallest nontrivial extension of n which is a cube.

Views

Author

Keywords

Links

Crossrefs

Programs

Python