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A345346 Primes whose digit reversal is twice a prime. 1
41, 43, 47, 83, 229, 241, 263, 283, 419, 431, 433, 439, 479, 491, 601, 607, 641, 643, 647, 661, 683, 811, 853, 857, 859, 877, 2039, 2063, 2069, 2083, 2099, 2203, 2207, 2251, 2273, 2281, 2287, 2411, 2417, 2423, 2437, 2467, 2473, 2617, 2621, 2663, 2671, 2677, 2683, 2687, 2689, 2801, 2819, 2837 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Karl-Heinz Hofmann, Table of n, a(n) for n = 1..10000

EXAMPLE

a(3) = 47 is a term because 47 and 74/2 = 37 are primes.

MAPLE

revdigs:= proc(n) local L, i;

  L:= convert(n, base, 10);

  add(L[-i]*10^(i-1), i=1..nops(L))

end proc:

filter:= proc(n) isprime(n) and numtheory:-bigomega(revdigs(n))=2 end proc:

select(filter, [seq(seq(seq(i*10^d+j, j=1..10^d-1, 2), i=2..8, 2), d=1..4)]);

PROG

(PARI) isok(p) = if (isprime(p), my(r=fromdigits(Vecrev(digits(p)))); if (!(r%2), isprime(r/2))); \\ Michel Marcus, Jun 15 2021

(Python) from sympy import isprime, primerange

def ok(p): t = int(str(p)[::-1]); return t%2 == 0 and isprime(t//2)

print(list(filter(ok, primerange(1, 2838)))) # Michael S. Branicky, Jun 16 2021

CROSSREFS

Intersection of A085778 and A273892.

Sequence in context: A154498 A223458 A243429 * A062669 A284290 A045710

Adjacent sequences:  A345343 A345344 A345345 * A345347 A345348 A345349

KEYWORD

nonn,base

AUTHOR

J. M. Bergot and Robert Israel, Jun 14 2021

STATUS

approved

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Last modified January 26 06:23 EST 2022. Contains 350572 sequences. (Running on oeis4.)