A346940 - OEIS

%I #18 Aug 31 2021 06:25:24

%S 2357,2582,3334,4714,5774,6667,8165,8819,9428,10542,10543,10544,10545,

%T 14907,14908,14909,18257,18258,18259,21081,21082,21083,23570,23571,

%U 25819,25820,27888,27889,29813,29814,31622,33332,33333,33335,33336,33337,33338,33339,33340,33341,33342

%N Numbers whose square starts with exactly 4 identical digits.

%C If m is a term, 10*m is another term.

%C Differs from A132391 where only at least 4 identical digits are required; indeed, 10541 is the first term of A132391 that is not in this sequence (see Example section), the next one is 33346.

%e 2357 is a term because 2357^2 = 5555449 starts with four 5's.

%e 10541 is not a term because 10541^2 = 111112681 starts with five 1's.

%t q[n_] := SameQ @@ (d = IntegerDigits[n^2])[[1 ;; 4]] && d[[5]] != d[[1]]; Select[Range[100, 33350], q] (* _Amiram Eldar_, Aug 08 2021 *)

%o (Python)

%o def ok(n):

%o     s = str(n*n)

%o     return len(s) > 4 and s[0] == s[1] == s[2] == s[3] != s[4]

%o print(list(filter(ok, range(33343)))) # _Michael S. Branicky_, Aug 08 2021

%Y Cf. A346941, A346942.

%Y Supersequences: A131573, A132391.

%Y Similar with: A346812 (2 digits), A346891 (3 digits).

%K nonn,base

%O 1,1

%A _Bernard Schott_, Aug 08 2021