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A074200
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a(n) = m, the smallest number such that (m+k)/k is prime for k=1, 2, ..., n.
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7
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1, 2, 12, 12720, 19440, 5516280, 5516280, 7321991040, 363500177040, 2394196081200, 3163427380990800, 22755817971366480, 3788978012188649280, 2918756139031688155200
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OFFSET
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1,2
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COMMENTS
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Computed by Jack Brennen and Phil Carmody.
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LINKS
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EXAMPLE
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(12+k)/k is prime for k = 1,2,3. 12 is the smallest such number so a(3) = 12.
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MATHEMATICA
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a[1] = 1; a[n_] := a[n] = For[dm = LCM @@ Range[n]; m = Quotient[a[n - 1], dm]*dm, True, m = m + dm, If[AllTrue[Range[n], PrimeQ[(m + #)/#] &], Return[m]]]; Table[an = a[n]; Print["a(", n, ") = ", an]; an, {n, 1, 10}] (* Jean-François Alcover, Dec 01 2016 *)
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PROG
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(PARI) isok(m, n) = {for (k = 1, n, if ((m+k) % k, return (0), if (! isprime((m+k)/k), return(0))); ); return (1); }
a(n) = {m = 1; while(! isok(m, n), m++); m; } \\ Michel Marcus, Aug 31 2013
(Python)
from sympy import isprime, lcm
a = lcm(range(1, n+1))
m = a
while True:
for k in range(n, 0, -1):
if not isprime(m//k+1):
break
else:
return m
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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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Jean-Christophe Colin (jc-colin(AT)wanadoo.fr), Sep 17 2002, May 10 2010
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EXTENSIONS
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STATUS
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approved
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