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 A343826 Numbers which are the product of two S-primes (A057948) in exactly one way. 4
 25, 45, 65, 81, 85, 105, 117, 145, 153, 165, 169, 185, 189, 205, 221, 245, 261, 265, 273, 285, 289, 297, 305, 333, 345, 357, 365, 369, 377, 385, 429, 445, 465, 477, 481, 485, 493, 505, 513, 533, 545, 549, 561, 565, 605, 609, 621, 629, 637, 645, 657, 665, 685 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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..3786 FORMULA a(n) == 1 (mod 4). - Hugo Pfoertner, May 01 2021 EXAMPLE 153 = 9*17 which are both S-primes, 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)) == 1; \\ Michel Marcus, May 01 2021 CROSSREFS Cf. A054520, A057948, A057949, A057950. Exactly two ways: A343827. Exactly three ways: A343828. Sequence in context: A015911 A188005 A054520 * A339958 A192261 A038811 Adjacent sequences: A343823 A343824 A343825 * A343827 A343828 A343829 KEYWORD nonn AUTHOR Zachary DeStefano, Apr 30 2021 STATUS approved

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Last modified June 22 14:17 EDT 2024. Contains 373587 sequences. (Running on oeis4.)