This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A077572 #17 Sep 29 2024 21:09:37
%S A077572 4,8,9,44,88,99,333,444,666,888,999,4444,8888,9999,44444,88888,99999,
%T A077572 333333,444444,666666,777777,888888,999999,4444444,8888888,9999999,
%U A077572 44444444,88888888,99999999,111111111,222222222,333333333,444444444
%N A077572 Nonsquarefree numbers obtained by repeating a single digit.
%e A077572 666 and 111111111 are members but 66, 1111 etc. are not.
%t A077572 Select[Flatten[Table[FromDigits[PadRight[{},i,n]],{i,9},{n,9}]],!SquareFreeQ[#]&] (* _Harvey P. Dale_, Jan 22 2013 *)
%o A077572 (Python)
%o A077572 from sympy.ntheory.factor_ import core
%o A077572 def repsthru(maxd):
%o A077572 yield from (int(di*d) for d in range(1, maxd+1) for di in "123456789")
%o A077572 def okrep(r): return r > 3 and core(r, 2) != r
%o A077572 print(list(filter(okrep, repsthru(9)))) # _Michael S. Branicky_, Apr 08 2021
%Y A077572 Cf. A077571, A087094.
%Y A077572 Subsequence of A013929 and A035132.
%K A077572 base,easy,nonn
%O A077572 1,1
%A A077572 _Amarnath Murthy_, Nov 11 2002
%E A077572 Corrected and extended by _Ray Chandler_, Aug 12 2003
%E A077572 Offset changed by _Andrew Howroyd_, Sep 29 2024