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A249589
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Numbers whose square with initial (= leftmost) digit removed is a prime.
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2
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5, 17, 19, 21, 23, 27, 29, 31, 33, 39, 49, 51, 53, 69, 71, 77, 79, 87, 91, 97, 143, 147, 151, 157, 159, 163, 171, 173, 187, 191, 199, 201, 229, 231, 233, 239, 241, 243, 247, 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
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OFFSET
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1,1
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COMMENTS
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LINKS
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MATHEMATICA
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Select[Range[600], PrimeQ[FromDigits[Rest[IntegerDigits[#^2]]]]&] (* Harvey P. Dale, Dec 13 2015 *)
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 *)
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PROG
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(PARI) is=(n)->isprime(n^2%10^(#Str(n^2)-1))
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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