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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Andreas Boe, Table of n, a(n) for n = 1..10766

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

Adjacent sequences:  A243746 A243747 A243748 * A243750 A243751 A243752

KEYWORD

nonn,base

AUTHOR

Andreas Boe, Jun 09 2014

STATUS

approved

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Last modified April 16 18:53 EDT 2021. Contains 343050 sequences. (Running on oeis4.)