A017981 Powers of cube root of 2 rounded up.

1, 2, 2, 2, 3, 4, 4, 6, 7, 8, 11, 13, 16, 21, 26, 32, 41, 51, 64, 81, 102, 128, 162, 204, 256, 323, 407, 512, 646, 813, 1024, 1291, 1626, 2048, 2581, 3251, 4096, 5161, 6502, 8192, 10322, 13004, 16384, 20643, 26008, 32768, 41286, 52016, 65536, 82571, 104032

Offset

0,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Mathematica

Table[Ceiling[(2^(1/3))^n], {n, 0, 300}] (* Vincenzo Librandi, Jan 05 2014 *)

Prog

(PARI) a(n) = ceil(sqrtn(2, 3)^n); \\ Michel Marcus, Jan 03 2014
(Python)
def icbrt(a):
    sr = 1 << (int.bit_length(int(a)) >> 1)
    while a < sr*sr*sr:  sr>>=1
    b = sr>>1
    while b:
      s = sr+b
      if a >= s*s*s:  sr = s
      b>>=1
    return sr
for n in range(100):  print(1+icbrt(2**n-1), end=", ")
# Alex Ratushnyak, Jan 04 2014
(Magma) [Ceiling(2^(n/3)): n in [1..60]]; // Vincenzo Librandi, Jan 05 2014

Crossrefs

Cf. A017979.

Sequence in context: A035381 A096938 A130084 * A274759 A274157 A005863

Adjacent sequences: A017978 A017979 A017980 * A017982 A017983 A017984

Keyword

nonn

Author

N. J. A. Sloane.

Extensions

a(44)-a(50) from Alex Ratushnyak, Jan 02 2014

Status

approved