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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
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
Exactly two ways: A343827. Exactly three ways: A343828.
Sequence in context: A015911 A188005 A054520 * A339958 A192261 A038811
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.)