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 A109373 Semiprimes of the form semiprime + 1. 9
 10, 15, 22, 26, 34, 35, 39, 58, 86, 87, 94, 95, 119, 122, 123, 134, 142, 143, 146, 159, 178, 202, 203, 206, 214, 215, 218, 219, 254, 299, 302, 303, 327, 335, 362, 382, 394, 395, 446, 447, 454, 482, 502, 515, 527, 538, 543, 554, 566, 623, 634, 635, 695, 698 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 FORMULA a(n) is in this sequence iff a(n) is in A001358 and (a(n)-1) is in A001358. a(n) = A070552(n) + 1. EXAMPLE a(1) = 10 because (3*3+1)=(2*5) = 10. a(2) = 15 because (2*7+1)=(3*5) = 15. a(3) = 22 because (3*7+1)=(2*11) = 22. a(4) = 26 because (5*5+1)=(2*13) = 26. a(5) = 34 because (3*11+1)=(2*17) = 34. MATHEMATICA fQ[n_] := Plus @@ Last /@ FactorInteger[n] == 2; Select[ Range[ 700], fQ[ # - 1] && fQ[ # ] &] (* Robert G. Wilson v *) With[{sps=Select[Range, PrimeOmega[#]==2&]}, Transpose[Select[ Partition[ sps, 2, 1], #[]-#[]==1&]][]] (* Harvey P. Dale, Sep 05 2012 *) PROG (Haskell) a109373 n = a109373_list !! (n-1) a109373_list = filter ((== 1) . a064911) a088707_list -- Reinhard Zumkeller, Feb 20 2012 (PARI) is(n)=bigomega(n)==2 && bigomega(n-1)==2 \\ Charles R Greathouse IV, Jan 31 2017 CROSSREFS Primes are in A000040. Semiprimes are in A001358. Primes of the form semiprime + 1 are in A005385 (safe primes). Semiprimes of the form semiprime + 1 are in this sequence. 3-almost primes of the form semiprime + 1 are in A109067. 4-almost primes of the form semiprime + 1 are in A109287. 5-almost primes of the form semiprime + 1 are in A109383. Least n-almost prime of the form semiprime + 1 are in A128665. Cf. A056809, A077065, A079148, A086005, A086006, A092307. Subsequence of A088707; A064911. Sequence in context: A115682 A075523 A115679 * A267329 A120138 A050200 Adjacent sequences:  A109370 A109371 A109372 * A109374 A109375 A109376 KEYWORD easy,nonn AUTHOR Jonathan Vos Post, Aug 24 2005 EXTENSIONS Extended by Ray Chandler and Robert G. Wilson v, Aug 25 2005 Edited by Ray Chandler, Mar 20 2007 STATUS approved

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Last modified August 4 01:57 EDT 2020. Contains 336201 sequences. (Running on oeis4.)