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A215659
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Values of k such that k*(k - 1) is a primorial number.
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5
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OFFSET
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1,1
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COMMENTS
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LINKS
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Carol Nelson, David E. Penney and Carl Pomerance, 714 and 715, J. Recreational Math. 7:2 (1994), pp. 87-89.
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FORMULA
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a(n) * (a(n) - 1) = A215658(n)#, where p# = 2 * 3 * 5 * 7 * 11 * ... * p is a primorial, the product of the primes from 2 to p.
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MATHEMATICA
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Select[Range[10^5], Product[Prime@ i, {i, PrimeNu@ #}] == # &[# (# - 1)] &] (* Michael De Vlieger, Apr 10 2018 *)
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PROG
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(Python)
from sympy import primorial, integer_nthroot
for i in range(1, 10**2):
a, b = integer_nthroot(4*primorial(i)+1, 2)
if b:
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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