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OFFSET
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1,2
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COMMENTS
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Erdős and Selfridge (1982) proved that if f(n) = primepi(a(n)) (or, equivalently, a(n) = prime(f(n))), then |f(n+1) - f(n)| <= 1, and that for infinitely many values of n, f(n+1) = f(n) - 1.
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LINKS
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Paul Erdős, Miscellaneous problems in number theory, Proceedings of the Eleventh Manitoba Conference on Numerical Mathematics and Computing (Winnipeg, Man., 1981), Congr. Numer., Vol. 34 (1982), pp. 25-45.
Paul Erdős and John L. Selfridge, Problem 6339, Advanced problems, The American Mathematical Monthly, Vol. 88, No. 4 (1981), p. 294; Factorizationf n!, solution to problem 6339, solved by the proposers, ibid., Vol. 89, No. 10 (1982), pp. 790-794.
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FORMULA
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Lim_{n->oo} a(n)/sqrt(n) = exp(gamma - 1/2), where gamma is Euler's constant (A001620) (Erdős and Selfridge, 1982).
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MATHEMATICA
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f[1] = 1; f[n_] := Module[{fct = FactorInteger[n], prods, ind}, prods = Rest @ FoldList[Times, 1, Power @@@ fct]; ind = FirstPosition[prods^2, _?(# > n &)][[1]]; fct[[ind, 1]]]; a[n_] := f[n!]; Array[a, 100]
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CROSSREFS
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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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