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 A280015 a(n) is the least k such that A056619(k) = prime(n). 0
 1, 2, 12, 10, 6, 76, 114, 34, 120, 246, 1386, 616, 1126, 3774, 510, 8220, 2634, 25810, 57936, 46836, 12180, 254940, 54574, 80040, 497146, 801780, 402324, 1003744, 6441196, 2858890, 27821214, 14312640, 47848164, 25049814, 8454126, 45433894, 4262890 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) is the least number that is a primitive root mod prime(n) but not mod any lower prime. Using the Chinese Remainder Theorem, it is easy to show that such k always exists. LINKS EXAMPLE 10 is a primitive root mod prime(4) = 7, but not mod 2, 3 or 5.  This is the least number with that property, so a(4)=10. MAPLE a[1]:= 1: a[2]:= 2: p:= 3: Cands:= {4, seq(seq(6*i+j, j=[0, 4]), i=1..10^7)}: for n from 3 while Cands <> {} do   p:= nextprime(p);   r:= numtheory:-primroot(p);   s:= select(t -> igcd(t, p-1)=1, {\$1..p-1});   q:= map(t -> r &^t mod p, s);   R, Cands:= selectremove(t -> member(t mod p, q), Cands):   if R = {} then break fi;   a[n]:= min(R); od: seq(a[i], i=1..n-1); CROSSREFS Cf. A056619. Sequence in context: A166544 A081468 A216349 * A245281 A308215 A216478 Adjacent sequences:  A280012 A280013 A280014 * A280016 A280017 A280018 KEYWORD nonn AUTHOR Robert Israel, Feb 21 2017 STATUS approved

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Last modified December 3 18:28 EST 2020. Contains 338911 sequences. (Running on oeis4.)