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A167735
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Primes that becomes a square when prefixed with a 2.
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8
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5, 89, 401, 601, 809, 1609, 2801, 4649, 5281, 6569, 9241, 9929, 14369, 18089, 19961, 21841, 27529, 33289, 41081, 43049, 51001, 61121, 67289, 73529, 79841, 84089, 92681, 94849
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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Select[Prime[Range[10000]], IntegerQ[Sqrt[FromDigits[Join[{2}, IntegerDigits[#]]]]]&] (* Harvey P. Dale, Dec 16 2010 *)
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PROG
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(PARI) \\ terms upto 10^n
upto(n) = {my(sqrt21 = sqrt(2.1), sqrt30 = sqrt(3.0), r, t=0);
for(k=2, n, for(j = ceil((sqrt21 * sqrt(10^k))), floor(sqrt30 * sqrt(10^k)),
r = j^2%10^k; if(isprime(r), t++; print1(r", ")))); t} \\ David A. Corneth, Jun 24 2016
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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