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 A333747 Numbers that are either the product of two consecutive primes or two primes with a prime in between. 3
 6, 10, 15, 21, 35, 55, 77, 91, 143, 187, 221, 247, 323, 391, 437, 551, 667, 713, 899, 1073, 1147, 1271, 1517, 1591, 1763, 1927, 2021, 2279, 2491, 2773, 3127, 3233, 3599, 3953, 4087, 4331, 4757, 4891, 5183, 5609, 5767, 6059, 6557, 7031, 7387, 8051, 8633, 8989, 9797, 9991 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS In other words, these are numbers that are the product of two distinct primes whose prime indices differ by at most two. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 FORMULA Union of A006094 and A090076. a(n) = prime(ceiling(n/2))*prime(ceiling((n+3)/2)). a(2*n-1) = prime(n)*prime(n+1). a(2*n) = prime(n)*prime(n+2). MAPLE R:= NULL; p:= 2; q:= 3; for n from 1 to 100 by 2 do r:= nextprime(q); R:= R, p*q, p*r; p:= q; q:= r; od: R; # Robert Israel, Apr 22 2020 MATHEMATICA a[n_] := Prime[Ceiling[n/2]] * Prime[Ceiling[(n + 3)/2]]; Array[a, 50] (* Amiram Eldar, Apr 04 2020 *) CROSSREFS Subsequence of A001358. Cf. A000040, A006094, A090076, A110654, A332765, A332877. Sequence in context: A211007 A315279 A122783 * A124000 A229321 A229323 Adjacent sequences: A333744 A333745 A333746 * A333748 A333749 A333750 KEYWORD nonn,easy AUTHOR Bobby Jacobs, Apr 03 2020 STATUS approved

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Last modified October 4 22:25 EDT 2023. Contains 365888 sequences. (Running on oeis4.)