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A067021 Largest prime of which the square still does not exceed the product of first n primes, the n-th primorial. 1
2, 5, 13, 47, 173, 709, 3109, 14929, 80429, 447829, 2724079, 17442769, 114379879, 784149077 (list; graph; refs; listen; history; internal format)
OFFSET

2,1

FORMULA

a(n)=Max[p; p^2 < A002110(n)], where p is prime; p(n+s)^2=a(n)^2<Product[p(1), ..., p(n)]<p(n+s+1)^2.

EXAMPLE

For n=2, 3, 4, 5, 7: {2^2, 6, 3^2}, {5^2, 30, 7^2}, {13^2, 210, 17^2}, {47^2, 2310, 53^2} {709^2, 510510, 719^2} or {4, 6, 9}, {25, 30, 49}, {169, 210, 289}, {2209, 2310, 2809}, {502681, 510510, 516961}. Also, if n=2, then a[2]<p(1)=2, if n=3, then a[3]=p(3)=5 but for n>3, a[n]>p(n+1), e.g. a[6]=p(40)=p(6+34)=173.

MATHEMATICA

q[x_] := Apply[Times, Table[Prime[w], {w, 1, x}]] rq[x_] := Floor[Sqrt[q[w]]//N] Table[Prime[PrimePi[a[w]]], {w, 2, 15}]

CROSSREFS

Cf. A002110, A067022.

Sequence in context: A111563 A079573 A194635 * A098716 A082938 A059103

Adjacent sequences:  A067018 A067019 A067020 * A067022 A067023 A067024

KEYWORD

nonn

AUTHOR

Labos E. (labos(AT)ana.sote.hu), Dec 29 2001

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Last modified February 17 03:18 EST 2012. Contains 205978 sequences.