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A258937
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Define f_i as the i-th iterate of A260187. a(n) is the least prime for which f_i(a(n)) is prime for all i such that 0 <= i < n and f_n(a(n)) is not prime.
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0
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2, 11, 41, 251, 2579, 32609, 543131, 10243031, 233336819, 6703033091, 207263540933, 7628002016027, 311878266460847, 13394639616667427, 628284422215925129, 33217442899664876729, 1955977793054900415107, 119244359152469819863541
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OFFSET
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1,1
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COMMENTS
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If p is prime, we replace p with A260187(p), until A260187(p) is not prime.
a(n) is the least prime for which the number of steps is n.
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LINKS
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EXAMPLE
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Trajectories of the first few terms:
2->0
11->5->1
41->11->5->1
251->41->11->5->1
2579->269->59->29->5->1
32609->2579->269->59->29->5->1
543131->32621->2591->281->71->11->5->1
10243031->543341->32831->2801->491->71->11->5->1
233336819->10243949->544259->33749->3719->1409->149->29->5->1
6703033091->233339861->10246991->547301->36791->6761->2141->41->11->5->1.
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PROG
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(PARI) a260187(n)=my(t=1, k); forprime(p=2, , k=t*p; if(k>n, return(n%t), t=k));
isok(k, n) = {for (j=1, n-1, nk = 260187(k); if (! isprime(nk), return (0)); k = nk; ); ! isprime(a260187(k)); }
a(n) = {my(k = 2); while(! isok(k, n), k = nextprime(k+1)); k; } \\ Michel Marcus, Nov 16 2015
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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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STATUS
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approved
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