cp's OEIS Frontend

A330281 Numbers whose prime-indices do not have weakly increasing numbers of distinct prime factors.

%I A330281 #8 Feb 07 2021 06:25:42
%S A330281 221,247,299,403,442,494,533,598,663,689,741,767,806,871,884,897,899,
%T A330281 988,1066,1079,1105,1189,1196,1209,1235,1261,1326,1339,1378,1417,1482,
%U A330281 1495,1517,1534,1537,1547,1599,1612,1651,1703,1711,1729,1742,1768,1794,1798
%N A330281 Numbers whose prime-indices do not have weakly increasing numbers of distinct prime factors.
%C A330281 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.
%H A330281 Amiram Eldar, <a href="/A330281/b330281.txt">Table of n, a(n) for n = 1..10000</a>
%e A330281 The sequence of terms together with their prime indices begins:
%e A330281    221: {6,7}
%e A330281    247: {6,8}
%e A330281    299: {6,9}
%e A330281    403: {6,11}
%e A330281    442: {1,6,7}
%e A330281    494: {1,6,8}
%e A330281    533: {6,13}
%e A330281    598: {1,6,9}
%e A330281    663: {2,6,7}
%e A330281    689: {6,16}
%e A330281    741: {2,6,8}
%e A330281    767: {6,17}
%e A330281    806: {1,6,11}
%e A330281    871: {6,19}
%e A330281    884: {1,1,6,7}
%e A330281 For example, 884 has prime indices {1,1,6,7} with numbers of distinct prime factors (0,0,2,1), which is not weakly increasing, so 884 belongs to the sequence.
%t A330281 Select[Range[1000],!OrderedQ[PrimeNu/@PrimePi/@First/@FactorInteger[#]]&]
%Y A330281 The version where prime factors are counted with multiplicity is A330103.
%Y A330281 Cf. A001221, A001222, A056239, A112798, A302242, A330098, A330230, A330233.
%K A330281 nonn
%O A330281 1,1
%A A330281 _Gus Wiseman_, Dec 10 2019