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A330947
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Nonprime numbers whose prime indices are all prime numbers.
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7
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1, 9, 15, 25, 27, 33, 45, 51, 55, 75, 81, 85, 93, 99, 121, 123, 125, 135, 153, 155, 165, 177, 187, 201, 205, 225, 243, 249, 255, 275, 279, 289, 295, 297, 327, 335, 341, 363, 369, 375, 381, 405, 415, 425, 451, 459, 465, 471, 495, 527, 531, 537, 545, 561, 573
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OFFSET
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1,2
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COMMENTS
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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.
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LINKS
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EXAMPLE
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The sequence of terms together with their prime indices of prime indices begins:
1: {}
9: {{1},{1}}
15: {{1},{2}}
25: {{2},{2}}
27: {{1},{1},{1}}
33: {{1},{3}}
45: {{1},{1},{2}}
51: {{1},{4}}
55: {{2},{3}}
75: {{1},{2},{2}}
81: {{1},{1},{1},{1}}
85: {{2},{4}}
93: {{1},{5}}
99: {{1},{1},{3}}
121: {{3},{3}}
123: {{1},{6}}
125: {{2},{2},{2}}
135: {{1},{1},{1},{2}}
153: {{1},{1},{4}}
155: {{2},{5}}
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MATHEMATICA
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Select[Range[100], !PrimeQ[#]&&And@@PrimeQ/@PrimePi/@First/@If[#==1, {}, FactorInteger[#]]&]
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CROSSREFS
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Nonprime numbers n such that A330944(n) = 0.
Taking odds instead of nonprimes gives A330946.
The number of prime prime indices is given by A257994.
Primes of nonprime index are A007821.
Products of primes of prime index are A076610.
Products of primes of nonprime index are A320628.
Numbers whose prime indices are not all prime are A330945.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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