Golf to find Boring numbers

Retina, 9 bytes

(.+)\1{4}

Verify all testcases! (slightly modified to run all testcases at once.)

05AB1E, 8 bytes

Code:

Œv¹y5×åO

Explanation:

Π        # Compute all substrings from the input.
 v        # For each substring.
   y5×    # Repeat the substring 5 times (42 × 5 = 4242424242).
  ¹   å   # Check if it's in the input string.
       O  # Sum up the result. Non-boring numbers should give 0.

Truthy is non-zero and falsy is zero. Uses the CP-1252 encoding.

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Java 8, 52 bytes

s->s.matches(".*(.+)\\1{4}.*")

Outgolfed this Java 8 answer with a direct String#matches.

Explanation:

Try it here.

s->              // Method with String parameter and boolean return-type
  s.matches(     //  Return whether the entire String matches the following regex:
    ".*          //   0 or more leading characters
     (.+)\\1{4}  //   group of 1 or more characters, repeated 5 times
     .*")        //   0 or more trailing characters