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%I #10 Dec 31 2016 01:26:40
%S 5,17,19,21,23,27,29,31,33,39,49,51,53,69,71,77,79,87,91,97,143,147,
%T 151,157,159,163,171,173,187,191,199,201,229,231,233,239,241,243,247,
%U 251,267,279,283,293,297,301,321,333,351,357,363,369,381,393,423,447,449,453,457,463,467,469,471,477,483,491,493,501,511,517,523
%N Numbers whose square with initial (= leftmost) digit removed is a prime.
%C The squares are in A225873.
%H Harvey P. Dale and Davin Park, <a href="/A249589/b249589.txt">Table of n, a(n) for n = 1..20000</a> [Terms 1 through 1000 were computed by Harvey P. Dale and terms 1001 through 20000 by Davin Park]
%t Select[Range[600],PrimeQ[FromDigits[Rest[IntegerDigits[#^2]]]]&] (* _Harvey P. Dale_, Dec 13 2015 *)
%t b /. Flatten[Outer[Solve[a + #2*10^#1 == b^2 && 0 <= a < 10^#1 && Sqrt[#2*10^#1] <= b < Sqrt[10^(#1 + 1)] && a \[Element] Primes, {a, b}, Integers] &, Range[0, 5], Range[9]], 2] (* _Davin Park_, Dec 30 2016 *)
%o (PARI) is=(n)->isprime(n^2%10^(#Str(n^2)-1))
%Y Cf. A227916, A225873.
%K nonn,base
%O 1,1
%A _M. F. Hasler_, Nov 01 2014
%E Extended by _Davin Park_, Dec 30 2016
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