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A330281
Numbers whose prime-indices do not have weakly increasing numbers of distinct prime factors.
2
221, 247, 299, 403, 442, 494, 533, 598, 663, 689, 741, 767, 806, 871, 884, 897, 899, 988, 1066, 1079, 1105, 1189, 1196, 1209, 1235, 1261, 1326, 1339, 1378, 1417, 1482, 1495, 1517, 1534, 1537, 1547, 1599, 1612, 1651, 1703, 1711, 1729, 1742, 1768, 1794, 1798
OFFSET
1,1
COMMENTS
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.
LINKS
EXAMPLE
The sequence of terms together with their prime indices begins:
221: {6,7}
247: {6,8}
299: {6,9}
403: {6,11}
442: {1,6,7}
494: {1,6,8}
533: {6,13}
598: {1,6,9}
663: {2,6,7}
689: {6,16}
741: {2,6,8}
767: {6,17}
806: {1,6,11}
871: {6,19}
884: {1,1,6,7}
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.
MATHEMATICA
Select[Range[1000], !OrderedQ[PrimeNu/@PrimePi/@First/@FactorInteger[#]]&]
CROSSREFS
The version where prime factors are counted with multiplicity is A330103.
Sequence in context: A266237 A371899 A159565 * A345512 A048931 A052478
KEYWORD
nonn
AUTHOR
Gus Wiseman, Dec 10 2019
STATUS
approved