Problem 53740. Easy Sequences 59: Almost Twin Primes
A positive integer pair
, is called an "almost twin prime pair", if one of the pair is a prime and the other is either a prime or a semiprime. A semiprime is a natural number that is a product of only two and exactly two (not necessarily distinct) prime numbers (e.g. 4, 6, 9,
,
,
,
,
,
...).
Listed below are all almost twin prime pairs with no element greater than
:
Our task in this exercise is, to create a function that counts the number of almost twin prime pairs whose elements are less than or equal to a given limit
Therefore for
, our function should return
.
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