A077572 Nonsquarefree numbers obtained by repeating a single digit.

4, 8, 9, 44, 88, 99, 333, 444, 666, 888, 999, 4444, 8888, 9999, 44444, 88888, 99999, 333333, 444444, 666666, 777777, 888888, 999999, 4444444, 8888888, 9999999, 44444444, 88888888, 99999999, 111111111, 222222222, 333333333, 444444444

Offset

0,1

Links

Table of n, a(n) for n=0..32.

Example

666 and 111111111 are members but 66, 1111 etc. are not.

Mathematica

Select[Flatten[Table[FromDigits[PadRight[{}, i, n]], {i, 9}, {n, 9}]], !SquareFreeQ[#]&] (* Harvey P. Dale, Jan 22 2013 *)

Prog

(Python)
from sympy.ntheory.factor_ import core
def repsthru(maxd):
  yield from (int(di*d) for d in range(1, maxd+1) for di in "123456789")
def okrep(r): return r > 3 and core(r, 2) != r
print(list(filter(okrep, repsthru(9)))) # Michael S. Branicky, Apr 08 2021

Crossrefs

Cf. A077571, A087094.

Subsequence of A013929 and A035132.

Sequence in context: A360758 A237607 A035132 * A239520 A083807 A098128

Adjacent sequences: A077569 A077570 A077571 * A077573 A077574 A077575

Keyword

base,easy,nonn

Author

Amarnath Murthy, Nov 11 2002

Extensions

Corrected and extended by Ray Chandler, Aug 12 2003

Status

approved