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 A337508 Primes such that neither the left half nor the right half of the prime is prime. 0
 11, 19, 41, 61, 89, 101, 109, 131, 139, 149, 151, 179, 181, 191, 199, 401, 409, 419, 421, 431, 439, 449, 461, 479, 491, 499, 601, 619, 631, 641, 659, 661, 691, 809, 811, 821, 829, 839, 859, 881, 911, 919, 929, 941, 971, 991, 1009, 1021, 1033, 1039, 1049, 1051 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For n > 9, the center digit is not considered when making the calculation. For a prime number to be in this sequence, both the substring to the left of the center and the substring to the right of the center must be nonprime. If a number appears in this sequence, it will not appear in A125523, A125524, or A125525. A000040 is the union of this sequence, A125523, A125524, and A125525. LINKS EXAMPLE 479 is prime. The left part of (4)79 is not prime. The right part of 47(9) is not prime. MAPLE q:= n-> isprime(n) and (s-> (h-> not ormap(x-> isprime(parse(x)),         [s[1..h], s[-h..-1]]))(iquo(length(s), 2)))(""||n): select(q, [\$11..2000])[];  # Alois P. Heinz, Sep 14 2020 PROG (PARI) lista(nn) = forprime(p=11, nn, my(l=#Str(p), e=floor(l/2), left=floor(p/10^(e+l%2)), right=p-floor(p/10^e)*10^e); if(!isprime(left) && !isprime(right), print1(p, ", "))) (Python) from sympy import nextprime, isprime A337508_list, p = [], 11 while p < 10**6:     s = str(p)     l = len(s)//2     if not (isprime(int(s[:l])) or isprime(int(s[-l:]))):         A337508_list.append(p)     p = nextprime(p) # Chai Wah Wu, Sep 14 2020 CROSSREFS Cf. A000040, A125523, A125524, A125525. Sequence in context: A154386 A066738 A278799 * A081027 A322474 A084986 Adjacent sequences:  A337505 A337506 A337507 * A337509 A337510 A337511 KEYWORD nonn,easy,base AUTHOR Iain Fox, Aug 30 2020 STATUS approved

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Last modified January 18 11:57 EST 2022. Contains 350455 sequences. (Running on oeis4.)