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 A174797 Numbers n such that both semiprime(n) and semiprime(n+1) are even. 2
 1, 4, 21, 87, 120, 141, 142, 168, 188, 320, 363, 387, 434, 464, 496, 539, 593, 675, 721, 794, 810, 995, 1032, 1105, 1147, 1166, 1228, 1356, 1391, 1477, 1478, 1498, 1702, 1771, 1790, 1797, 1803, 1818, 1849, 1850, 1881, 1967, 2016, 2039, 2052, 2065, 2091 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Semiprime(n)/2 and semiprime(n+1)/2 are consecutive primes. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..2000 FORMULA A001358(a(n)) = 2*A000040(A174798(n)). EXAMPLE a(1)=1 because both semiprime(1)=4 and semiprime(2)=6 are even a(2)=4 because both semiprime(4)=10 and semiprime(5)=14 are even. MATHEMATICA Flatten[Position[Partition[Select[Range[10000], PrimeOmega[#]==2&], 2, 1], _?(EvenQ[First[#]]&&EvenQ[Last[#]]&), {1}, Heads->False]] (* Harvey P. Dale, Apr 19 2014 *) CROSSREFS Cf. A000040, A001358, A174798. Sequence in context: A348621 A277794 A292126 * A328345 A371309 A220574 Adjacent sequences: A174794 A174795 A174796 * A174798 A174799 A174800 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Mar 29 2010 EXTENSIONS Edited and corrected by Ray Chandler, Apr 07 2010 STATUS approved

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Last modified August 13 15:31 EDT 2024. Contains 375142 sequences. (Running on oeis4.)