

A048975


Pairs of consecutive primes p, q, for which the smallest primitive root of q is 1 greater than the smallest primitive root of p.


0



2, 3, 5, 7, 13, 17, 29, 31, 83, 89, 131, 137, 197, 199, 211, 223, 317, 331, 349, 353, 443, 449, 461, 463, 509, 521, 563, 569, 587, 593, 613, 617, 619, 631, 727, 733, 797, 809, 821, 823, 853, 857, 877, 881, 947, 953, 967, 971, 983, 991, 991, 997, 1061, 1063
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OFFSET

1,1


REFERENCES

P. Ribenboim, The new book of prime number records, Springer 1996, 2225


LINKS

Table of n, a(n) for n=1..54.
Index entries for primes by primitive root


EXAMPLE

The primitive roots (mod 13) are 2, 6, 7, and 11, and the primitive roots (mod 17) are 3, 5, 6, 7, 10, 11, 12, and 14, so since 3 = 2 + 1, 13 and 17 are in the sequence.
991 is in the sequence twice because the smallest primitive roots for the three consecutive primes 983, 991, and 997 are 5, 6, and 7, respectively, so 991 appears as the larger of the pair (983,991) since 6 = 5 + 1, and as the smaller of the pair (991,997) since 7 = 6 + 1.


MATHEMATICA

Reap[ Do[ If[ PrimitiveRoot[p] + 1 == PrimitiveRoot[np = NextPrime[p]], Sow[p]; Sow[np]], {p, Prime /@ Range[200]}]][[2, 1]] (* JeanFrançois Alcover, Oct 04 2012 *)
Flatten[{Prime[#], Prime[#+1]}&/@Flatten[Position[Partition[ PrimitiveRoot[ Prime[ Range[200]]], 2, 1], _?(#[[2]]#[[1]]==1&), {1}, Heads>False]]] (* Harvey P. Dale, Dec 22 2014 *)


PROG

(PARI) forprime(p=2, 1061, if( lift(znprimroot(p)) + 1 == lift(znprimroot(nextprime(p+1))), print(p); print(nextprime(p+1)))) \\ Michael B. Porter, Mar 03 2013


CROSSREFS

Sequence in context: A092621 A188809 A152449 * A009571 A087520 A117159
Adjacent sequences: A048972 A048973 A048974 * A048976 A048977 A048978


KEYWORD

nice,nonn


AUTHOR

Felice Russo


EXTENSIONS

More terms from James A. Sellers, Apr 22 2000


STATUS

approved



