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A107439 a(1)=2, a(n) is the smallest prime > a(n-1) such that a(n) is a primitive root mod a(n-1) and vice versa. 1
2, 3, 5, 7, 17, 23, 89, 113, 137, 149, 163, 181, 191, 233, 257, 263, 277, 283, 397, 419, 421, 443, 449, 461, 463, 509, 557, 569, 593, 599, 613, 619, 701, 719, 821, 823, 829, 857, 863, 877, 919, 1097, 1103, 1117, 1171, 1181, 1193, 1213, 1237, 1259, 1361, 1367 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
if a(n) is 3 mod 4, then by quadratic reciprocity, if q is 3 mod 4, then either q is a square mod a(n) or vice versa, so a(n+1) must be 1 mod 4.
LINKS
EXAMPLE
a(5)=17 because 7 is a primitive root mod 17 and 17 (=3 mod 7) is a primitive root mod 7. Also a(5) is not 11 since 11 has order 3 mod 7, a(5) is not 13 since 13 has order 2 mod 7.
PROG
(PARI) first(n) = { my(res=vector(n)); res[1]=2; for(x=2, n, forprime(p=res[x-1]+1, , if(znorder(Mod(p, res[x-1]))==(res[x-1]-1) && znorder(Mod(res[x-1], p))==(p-1), res[x]=p; break()))); res; } \\ Iain Fox, Nov 29 2017
CROSSREFS
Sequence in context: A164042 A248344 A060212 * A262836 A356475 A178382
KEYWORD
nonn
AUTHOR
John L. Drost, May 26 2005
STATUS
approved

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Last modified July 13 12:04 EDT 2024. Contains 374282 sequences. (Running on oeis4.)