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 A109027 Numbers that have exactly seven prime factors counted with multiplicity (A046308) whose digit reversal is different and also has 7 prime factors (with multiplicity). 10
 8820, 21240, 21708, 21780, 21920, 23280, 23472, 23625, 23800, 25560, 25584, 25758, 26280, 27432, 27504, 27888, 27900, 28836, 29250, 29403, 29736, 29970, 30492, 34884, 36828, 40338, 40572, 40950, 41976, 42228, 42984, 43659, 43956, 44128 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This sequence is the k = 7 instance of the series which begins with k = 1 (emirps), k = 2, k = 3, k = 4, k = 5 (A109025), k = 6 (A109026). LINKS David A. Corneth, Table of n, a(n) for n = 1..10000 Eric Weisstein's World of Mathematics, Almost Prime. Eric Weisstein's World of Mathematics, Emirp. Eric Weisstein and Jonathan Vos Post, Emirpimes. EXAMPLE a(20) = 29403 is in this sequence because 29403 = 3^5 * 11^2 has exactly 7 prime factors counted with multiplicity and reverse(29403) = 30492 = 2^2 * 3^2 * 7 * 11^2 also has exactly 7 prime factors counted with multiplicity. MATHEMATICA Select[Range[45000], !PalindromeQ[#]&&PrimeOmega[#]==PrimeOmega[ IntegerReverse[ #]] ==7&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 02 2019 *) PROG (PARI) is(n) = { my(r = fromdigits(Vecrev(digits(n)))); n!=r && bigomega(n) == 7 && bigomega(r) == 7 } \\ David A. Corneth, Mar 07 2024 CROSSREFS Cf. A046308, A006567, A097393, A109018, A109023, A109024, A109025, A109026, A109028, A109029, A109030, A109031. Sequence in context: A270609 A230335 A183752 * A237761 A186582 A147529 Adjacent sequences: A109024 A109025 A109026 * A109028 A109029 A109030 KEYWORD nonn,base AUTHOR Jonathan Vos Post, Jun 16 2005 STATUS approved

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Last modified September 17 14:02 EDT 2024. Contains 375987 sequences. (Running on oeis4.)