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.

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

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