
We distinguish two related but fundamentally different short-interval problems: the occurrence of P_2-numbers, integers with at most two prime factors, and the occurrence of E_2-numbers, integers with exactly two prime factors. The former is accessible to classical weighted-sieve methods and is known in intervals much shorter than √x, while the latter is parity-sensitive in worst-case intervals. This paper proposes a heuristic framework for exact semiprimes in short intervals. The central observation is that local semiprime concentration is governed by two forces. The first is prime supply: after fixing a least prime factor p, exact semiprimes pq in (x, x+H] correspond to primes q in the scaled interval (x/p, (x+H)/p]. The second is factor-pair multiplicity: summing over possible least-prime-factor lanes contributes the harmonic multiplier sum_{p ≤ √x} 1/p ~ log log x. Together these forces predict #{m ∈ (x, x+H] : Ω(m) = 2} ≈ H · (log log x) / log x. However, this prediction is already vastly weaker than known almost-all results in typical intervals, and it does not by itself overcome the parity barrier in worst-case intervals. We therefore frame the main problem as a worst-case exact-semiprime gap problem: whether E_2-numbers have no √x-scale gaps, and in particular whether every sufficiently large interval (n², (n+1)²) contains an exact semiprime. An exact enumeration of Ω(n) for all n < 10^11 supports the framework: the local density matches the prediction up to a stable lower-order correction, the worst-case gap grows like (1/4)(log x)² — three to four orders of magnitude below √x — and every consecutive square interval below 10^11 contains an exact semiprime, with counts parity-symmetric and bounded well away from zero.
Legendre's conjecture, sieve methods, prime gaps, short intervals, semiprimes, least prime factors, consecutive squares, almost primes, parity barrier
Legendre's conjecture, sieve methods, prime gaps, short intervals, semiprimes, least prime factors, consecutive squares, almost primes, parity barrier
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