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A375964
Semiprime numbers that are sandwiched between products of exactly 4 distinct primes (or tetraprimes).
0
41614, 51358, 55166, 67066, 97054, 97294, 100834, 101914, 109838, 122758, 126634, 130646, 133286, 148394, 154582, 175594, 180214, 180454, 184666, 197086, 212486, 224258, 226654, 227446, 231386, 242906, 258446, 276394, 284866, 285086, 300182, 305066, 308606, 309506, 317054, 344434, 350206, 352834, 360634, 362594
OFFSET
1,1
FORMULA
a(n) == 2 (mod 4).
EXAMPLE
41614 = 2 * 20807 (between 41613 = 3*11*13*97 and 41615 = 5*7*29*41).
51358 = 2 * 25679 (between 51357 = 3*17*19*53 and 51359 = 7*11*23*29).
55166 = 2 * 27583 (between 55165 = 5*11*17*59 and 55167 = 3*7*37*71).
MATHEMATICA
e[n_] := FactorInteger[n][[;; , 2]]; SequencePosition[e /@ Range[400000], {{1, 1, 1, 1}, {1, 1}, {1, 1, 1, 1}}][[;; , 1]] + 1 (* Amiram Eldar, Sep 04 2024 *)
CROSSREFS
Subsequence of A100484.
Sequence in context: A002879 A207049 A236482 * A163392 A262801 A253681
KEYWORD
nonn
AUTHOR
Massimo Kofler, Sep 04 2024
STATUS
approved