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A304390 Prime numbers p such that p squared + (p reversed) squared is also prime. 2
23, 41, 227, 233, 283, 401, 409, 419, 421, 461, 491, 499, 823, 827, 857, 877, 2003, 2083, 2267, 2437, 2557, 2593, 2617, 2633, 2677, 2857, 2887, 2957, 4001, 4021, 4051, 4079, 4129, 4211, 4231, 4391, 4409, 4451, 4481, 4519, 4591, 4621, 4639, 4651, 4871, 6091, 6301, 6329, 6379, 6521, 6529, 6551 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..5000

EXAMPLE

The prime number 227 belongs to this sequence as 722 is 227 reversed and 227^2 + 722^2 = 572813, which is prime.

MATHEMATICA

Select[Prime@ Range@ 850, PrimeQ[#^2 + FromDigits[ Reverse@ IntegerDigits@ #]^2] &] (* Giovanni Resta, Sep 03 2018 *)

PROG

(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):

    r=int((str(i)[::-1]))

    t=pow(i, 2)+pow(r, 2)

    if is_prime(i):

       if is_prime(t):

          ris = ris+str(i)+", "

print(ris)

(PARI) isok(p) = isprime(p) && isprime(p^2+eval(fromdigits(Vecrev(digits(p))))^2); \\ Michel Marcus, Aug 21 2018

CROSSREFS

Cf. A061783 (Luhn primes).

Subsequence of A069207. - Michel Marcus, Aug 21 2018

Sequence in context: A155702 A114379 A106969 * A309533 A306085 A037137

Adjacent sequences:  A304387 A304388 A304389 * A304391 A304392 A304393

KEYWORD

nonn,base

AUTHOR

Pierandrea Formusa, Aug 16 2018

STATUS

approved

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Last modified September 17 04:58 EDT 2019. Contains 327119 sequences. (Running on oeis4.)