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 A343827 Numbers which are the product of two S-primes (A057948) in exactly two ways. 4
 441, 693, 1089, 1197, 1449, 1617, 1881, 1953, 2277, 2541, 2709, 2793, 2961, 3069, 3249, 3381, 3717, 3933, 4221, 4257, 4473, 4557, 4653, 4761, 4977, 5229, 5301, 5841, 5929, 6321, 6417, 6489, 6633, 6741, 6897, 6909, 7029, 7353, 7581, 7821, 8001, 8037, 8217, 8253 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS First differs from A057950 at a(21)=4473, whereas A057950(21)=4389, which can be represented as the product of two S-primes in exactly 3 ways. There exist numbers which are the product of two S-primes in exactly 1, 2, and 3 ways; however, it is unknown if any numbers exist which are the product of two S-primes in exactly 4 ways. LINKS Zachary DeStefano, Table of n, a(n) for n = 1..2484 FORMULA a(n) == 1 (mod 4). - Hugo Pfoertner, May 01 2021 EXAMPLE 1449=9*161=21*69 which are all S-primes (A057948), and admits no other S-prime factorizations. PROG (PARI) \\ uses is(n) from A057948 isok(n) = sumdiv(n, d, (d<=n/d) && is(d) && is(n/d)) == 2; \\ Michel Marcus, May 01 2021 CROSSREFS Cf. A054520, A057948, A057949, A057950. Exactly one way: A343826. Exactly three ways: A343828. Sequence in context: A252194 A057949 A057950 * A250808 A202400 A014793 Adjacent sequences: A343824 A343825 A343826 * A343828 A343829 A343830 KEYWORD nonn AUTHOR Zachary DeStefano, Apr 30 2021 STATUS approved

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