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 A321494 Numbers k such that k and k+1 have at least 4 but not both exactly 4 distinct prime factors. 7
 38570, 40754, 51414, 51765, 58695, 60605, 62985, 66044, 68585, 70889, 71070, 73185, 73814, 74865, 77349, 82004, 83265, 83720, 83979, 85085, 87009, 90804, 90915, 91805, 91884, 92378, 94094, 94829, 96459, 97565, 98769, 98889, 100814, 101269, 101660, 104005, 104754, 105468, 107184, 108030, 108185, 108965 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A321504 lists numbers n such that k and k+1 both have at least 4 distinct prime factors, while A140078 lists numbers such that k and k+1 have exactly 4 distinct prime factors. This sequence is the complement of the latter in the former, it consists of terms with indices (124, 214, 219, 276, 321, 415, ...) of the former. LINKS Table of n, a(n) for n=1..42. FORMULA A321504 \ A140078. MATHEMATICA aQ[n_]:=Module[{v={PrimeNu[n], PrimeNu[n+1]}}, Min[v]>3 && v!={4, 4}]; Select[Range[120000], aQ] (* Amiram Eldar, Nov 12 2018 *) PROG (PARI) is(n)=vecmin(n=[omega(n), omega(n+1)])>=4&&n!=[4, 4] CROSSREFS Cf. A140078, A321504; A321493, A321496 (analog for 3 & 5 factors). Sequence in context: A362217 A330427 A289824 * A252103 A074484 A186583 Adjacent sequences: A321491 A321492 A321493 * A321495 A321496 A321497 KEYWORD nonn AUTHOR M. F. Hasler, Nov 12 2018 STATUS approved

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Last modified July 19 16:24 EDT 2024. Contains 374410 sequences. (Running on oeis4.)