

A339361


Product of prime indices of the nth squarefree semiprime.


6



2, 3, 4, 6, 8, 5, 6, 10, 7, 12, 8, 12, 9, 14, 15, 16, 10, 11, 18, 18, 12, 20, 13, 21, 14, 20, 24, 22, 15, 24, 16, 24, 27, 17, 28, 18, 26, 28, 32, 19, 30, 20, 30, 30, 21, 33, 22, 32, 36, 23, 34, 24, 36, 36, 35, 25, 38, 26, 40, 39, 27, 40, 40, 28, 42, 44, 29, 42
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OFFSET

1,1


COMMENTS

A squarefree semiprime (A006881) is a product of any two distinct prime numbers. A prime index of n is a number m such that the mth prime number divides n. The multiset of prime indices of n is row n of A112798.


LINKS



FORMULA



EXAMPLE

The sequence of all squarefree semiprimes together with the products of their prime indices begins:
6: 1 * 2 = 2
10: 1 * 3 = 3
14: 1 * 4 = 4
15: 2 * 3 = 6
21: 2 * 4 = 8
22: 1 * 5 = 5
26: 1 * 6 = 6
33: 2 * 5 = 10
34: 1 * 7 = 7
35: 3 * 4 = 12


MATHEMATICA

Table[Times@@PrimePi/@First/@FactorInteger[n], {n, Select[Range[100], SquareFreeQ[#]&&PrimeOmega[#]==2&]}]


CROSSREFS

A003963 gives the product of prime indices of n.
A006881 lists squarefree semiprimes.
A025129 is the sum of squarefree semiprimes of weight n.
A332765/A339114 give the greatest/least squarefree semiprime of weight n.
A338905 groups squarefree semiprimes by weight.
A339116 groups squarefree semiprimes by greater prime factor.
Cf. A001221, A046388, A056239 (weight), A112798, A166237, A320656, A320911, A338901, A339002, A339003, A339004.


KEYWORD

nonn


AUTHOR



STATUS

approved



