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A317650
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The n-th term is the smallest integer > 1 that is congruent to +1 or -1 modulo k for all 2 <= k <= n.
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0
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3, 5, 5, 11, 11, 29, 41, 71, 71, 881, 1079, 10009, 10009, 32759, 82081, 636481, 636481, 2162161, 2162161, 2162161, 2162161, 39412801, 39412801, 39412801, 39412801, 1074427199, 1074427199, 15362146799, 15362146799, 109271408401, 482955026399, 482955026399
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OFFSET
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2,1
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LINKS
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MATHEMATICA
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Rest@ Nest[Function[a, Append[a, Block[{k = a[[-1]]}, While[! AllTrue[Table[Or[# == 1, # == m - 1] &@ Mod[k, m], {m, Length@ a + 1}], # &], k++]; k]]], {2}, 16] (* Michael De Vlieger, Aug 02 2018 *)
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PROG
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(PARI)
ok(n, m)={for(i=2, n, my(r=m%i); if(r<>1&&r<>i-1, return(0))); 1}
a(n)={my(m=oo, p=primes(primepi(n))); p=vector(#p, i, p[i]^logint(n, p[i]));
for(k=0, 2^#p-1, my(t=2+lift(-2+chinese(vector(#p, i, Mod(if(bittest(k, i-1), -1, 1), p[i]))))); if(t<m && ok(n, t), m=t)); m} \\ Andrew Howroyd, Aug 02 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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