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 A037143 Numbers with at most 2 prime factors (counted with multiplicity). 34
 1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 13, 14, 15, 17, 19, 21, 22, 23, 25, 26, 29, 31, 33, 34, 35, 37, 38, 39, 41, 43, 46, 47, 49, 51, 53, 55, 57, 58, 59, 61, 62, 65, 67, 69, 71, 73, 74, 77, 79, 82, 83, 85, 86, 87, 89, 91, 93, 94, 95, 97, 101, 103, 106, 107, 109, 111, 113, 115, 118 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A001222(a(n)) <= 2; A054576(a(n)) = 1. - Reinhard Zumkeller, Mar 10 2006 Products of two noncomposite numbers. - Juri-Stepan Gerasimov, Apr 15 2010 Also numbers such that exist permutations of all divisors only with coprime adjacent elements: A109810(a(n))>0. - Reinhard Zumkeller, May 24 2010 A060278(a(n)) = 0. - Reinhard Zumkeller, Apr 05 2013 1 together with numbers n such that sigma(n)+phi(n)-d(n) = 2n-2. - Wesley Ivan Hurt, May 03 2015 LINKS R. Zumkeller, Table of n, a(n) for n = 1..1000 MAPLE with(numtheory): A037143:=n->`if`(bigomega(n)<3, n, NULL): seq(A037143(n), n=1..200); # Wesley Ivan Hurt, May 03 2015 MATHEMATICA Select[Range[120], PrimeOmega[#] <= 2 &] (* Ivan Neretin, Aug 16 2015 *) PROG (Haskell) a037143 n = a037143_list !! (n-1) a037143_list = 1 : merge a000040_list a001358_list where    merge xs'@(x:xs) ys'@(y:ys) =          if x < y then x : merge xs ys' else y : merge xs' ys -- Reinhard Zumkeller, Dec 18 2012 (PARI) is(n)=bigomega(n)<3 \\ Charles R Greathouse IV, Apr 29 2015 CROSSREFS Union of A008578 and A001358. Complement of A033942. Cf. A063928, A001222, A054576, A109810, A060278. A101040(a(n))=1 for n>1. Subsequence of A037144. - Reinhard Zumkeller, May 24 2010 A098962 and A139690 are subsequences. Sequence in context: A325457 A063538 A167207 * A236105 A292050 A048627 Adjacent sequences:  A037140 A037141 A037142 * A037144 A037145 A037146 KEYWORD nonn AUTHOR EXTENSIONS More terms from Henry Bottomley, Aug 15 2001 STATUS approved

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Last modified August 11 06:25 EDT 2020. Contains 336422 sequences. (Running on oeis4.)