A077572 - OEIS

%I #17 Sep 29 2024 21:09:37

%S 4,8,9,44,88,99,333,444,666,888,999,4444,8888,9999,44444,88888,99999,

%T 333333,444444,666666,777777,888888,999999,4444444,8888888,9999999,

%U 44444444,88888888,99999999,111111111,222222222,333333333,444444444

%N Nonsquarefree numbers obtained by repeating a single digit.

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

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

%o (Python)

%o from sympy.ntheory.factor_ import core

%o def repsthru(maxd):

%o   yield from (int(di*d) for d in range(1, maxd+1) for di in "123456789")

%o def okrep(r): return r > 3 and core(r, 2) != r

%o print(list(filter(okrep, repsthru(9)))) # _Michael S. Branicky_, Apr 08 2021

%Y Cf. A077571, A087094.

%Y Subsequence of A013929 and A035132.

%K base,easy,nonn,changed

%O 1,1

%A _Amarnath Murthy_, Nov 11 2002

%E Corrected and extended by _Ray Chandler_, Aug 12 2003

%E Offset changed by _Andrew Howroyd_, Sep 29 2024