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Numbers whose square has initial digit '2'.
2

%I #21 Apr 15 2024 20:35:35

%S 5,15,16,17,45,46,47,48,49,50,51,52,53,54,142,143,144,145,146,147,148,

%T 149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,

%U 166,167,168,169,170,171,172,173,448,449,450,451,452,453,454,455,456

%N Numbers whose square has initial digit '2'.

%H Seiichi Manyama, <a href="/A045856/b045856.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range[500],IntegerDigits[#^2][[1]]==2&] (* _Harvey P. Dale_, Apr 15 2024 *)

%o (PARI) isok(n) = digits(n^2)[1] == 2; \\ _Michel Marcus_, May 28 2017

%Y Cf. A045785

%K nonn,base

%O 1,1

%A _Jeff Burch_

%E Corrected by _Seiichi Manyama_, May 28 2017