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A344296 Numbers with at least as many prime factors (counted with multiplicity) as half their sum of prime indices. 24

%I #13 May 20 2021 23:05:33

%S 1,2,3,4,6,8,9,10,12,16,18,20,24,27,28,30,32,36,40,48,54,56,60,64,72,

%T 80,81,84,88,90,96,100,108,112,120,128,144,160,162,168,176,180,192,

%U 200,208,216,224,240,243,252,256,264,270,280,288,300,320,324,336,352

%N Numbers with at least as many prime factors (counted with multiplicity) as half their sum of prime indices.

%C A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

%C These are the Heinz numbers of certain partitions counted by A025065, but different from palindromic partitions, which have Heinz numbers A265640.

%F A056239(a(n)) <= 2*A001222(a(n)).

%F a(n) = A322136(n)/4.

%e The sequence of terms together with their prime indices begins:

%e 1: {} 30: {1,2,3}

%e 2: {1} 32: {1,1,1,1,1}

%e 3: {2} 36: {1,1,2,2}

%e 4: {1,1} 40: {1,1,1,3}

%e 6: {1,2} 48: {1,1,1,1,2}

%e 8: {1,1,1} 54: {1,2,2,2}

%e 9: {2,2} 56: {1,1,1,4}

%e 10: {1,3} 60: {1,1,2,3}

%e 12: {1,1,2} 64: {1,1,1,1,1,1}

%e 16: {1,1,1,1} 72: {1,1,1,2,2}

%e 18: {1,2,2} 80: {1,1,1,1,3}

%e 20: {1,1,3} 81: {2,2,2,2}

%e 24: {1,1,1,2} 84: {1,1,2,4}

%e 27: {2,2,2} 88: {1,1,1,5}

%e 28: {1,1,4} 90: {1,2,2,3}

%t Select[Range[100],PrimeOmega[#]>=Total[Cases[FactorInteger[#],{p_,k_}:>k*PrimePi[p]]]/2&]

%Y The case with difference at least 1 is A322136.

%Y The case of equality is A340387, counted by A000041 or A035363.

%Y The opposite version is A344291, counted by A110618.

%Y The conjugate version is A344414, with even-weight case A344416.

%Y A025065 counts palindromic partitions, ranked by A265640.

%Y A056239 adds up prime indices, row sums of A112798.

%Y A300061 lists numbers whose sum of prime indices is even.

%Y Cf. A001399, A002865, A025147, A027336, A036036, A067712, A244990, A261144, A325691, A344293, A344295.

%K nonn

%O 1,2

%A _Gus Wiseman_, May 16 2021

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Last modified May 21 15:47 EDT 2024. Contains 372738 sequences. (Running on oeis4.)