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A113530 Semiprimes in A003215. 8
91, 169, 217, 469, 721, 817, 1027, 1141, 1261, 1387, 2611, 2977, 3781, 3997, 4681, 5677, 5941, 6487, 6769, 7651, 7957, 8587, 9577, 10981, 11347, 12481, 12871, 14077, 14491, 15769, 16207, 17557, 18019, 18961, 20419, 20917, 21421, 22969, 24031 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Intersection of A003215 and A001358.
LINKS
EXAMPLE
a(1) = 91 because A003215(5) = (5+1)^3 - 5^3 = 91 = 7 * 13 is semiprime.
a(7) = 121 because A003215(7) = (7+1)^3 - 7^3 = 169 = 13^2 is semiprime; the two prime factors need not be distinct.
MATHEMATICA
Select[Array[3 #^2 + 3 # + 1 &, 90], PrimeOmega[#] == 2 &] (* Michael De Vlieger, Mar 17 2021 *)
CROSSREFS
Sequence in context: A293647 A225908 A159961 * A119148 A166059 A226683
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Jan 12 2006
STATUS
approved

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Last modified May 29 21:02 EDT 2024. Contains 372952 sequences. (Running on oeis4.)