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A243749
Semiprimes which are products of two primes each with half the number of digits, and which when split in the middle gives two primes; no leading zeros.
1
25, 35, 1147, 1159, 1189, 1343, 1711, 1943, 1961, 2911, 2923, 3713, 4171, 4183, 4189, 4331, 4717, 5329, 5917, 101263, 101461, 101617, 101659, 101887, 101911, 101971, 103127, 103223, 103277, 103283, 103331, 103373, 103463, 103487, 103601, 103709, 103739, 103877
OFFSET
1,1
EXAMPLE
1961=37*53 has 4 digits and is the product of two 2-digit primes, and 1961 -> 19 and 61 also gives two 2-digit primes.
PROG
(PARI) isok(n) = (bigomega(n) == 2) && (len = #Str(n)) && !(len % 2) && (f=factor(n)) && prod(i=1, #f~, #Str(f[i, 1])== len/2) && isprime(n\10^(len/2)) && isprime(q=n % 10^(len/2)) && (#Str(q)== len/2); \\ Michel Marcus, Jun 10 2014
CROSSREFS
Sequence in context: A331808 A153446 A039457 * A331143 A031366 A068165
KEYWORD
nonn,base
AUTHOR
Andreas Boe, Jun 09 2014
STATUS
approved