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A319141
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Prime numbers p such that p squared + p reversed is also prime.
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1
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211, 223, 271, 283, 433, 463, 691, 823, 859, 2017, 2029, 2251, 2269, 2293, 2341, 2347, 2593, 2647, 2833, 2851, 2857, 2887, 4153, 4327, 4507, 4513, 4903, 6091, 6361, 6421, 6481, 6529, 6871, 6949, 8011, 8059, 8161, 8209, 8287, 8419, 8467, 8707, 8803, 8929, 8971
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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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EXAMPLE
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271 belongs to this sequence as 271 squared is 73441 and 271 reversed is 172 and the sum of 73441 and 172 is 73613, which is prime.
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MAPLE
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revdigs:= proc(n) local L, i;
L:= convert(n, base, 10);
add(L[-i]*10^(i-1), i=1..nops(L));
end proc:
filter:= t -> isprime(t) and isprime(t^2+revdigs(t)):
select(filter, [seq(t, t=1..10^4, 6)]); # Robert Israel, Sep 13 2018
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MATHEMATICA
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Select[Prime@Range@1120, PrimeQ[#^2 + FromDigits[Reverse@IntegerDigits@#]] &] (* Vincenzo Librandi, Sep 14 2018 *)
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PROG
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(Python)
nmax=10000
def is_prime(num):
if num == 0 or num == 1: return(0)
for k in range(2, num):
if (num % k) == 0:
return(0)
return(1)
ris = ""
for i in range(nmax):
if is_prime(i):
r=int((str(i)[::-1]))
t=pow(i, 2)+r
if is_prime(t):
ris = ris+str(i)+", "
print(ris)
(PARI) forprime(p=1, 9000, if(ispseudoprime(p^2 + eval(concat(Vecrev(Str(p))))), print1(p, ", "))) \\ Felix Fröhlich, Sep 12 2018
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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