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A323713 a(n) = beginning of a run of at least n primes when x -> 3*x - 2 is iterated. 0
2, 3, 3, 5, 61, 1171241, 1197631, 25451791, 25451791, 9560914721, 9560914721, 860964705721, 185133795875771 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For n > 4, a(n) == 1 (mod 10).

LINKS

Table of n, a(n) for n=1..13.

EXAMPLE

a(4) = 5 because 5 is the beginning of 4 primes in succession: 5, 3*5 - 2 = 13 is prime, 3*13 - 2 = 37 is prime, 3*37 - 2 = 109 is prime.

MATHEMATICA

c[p_] := Block[{k=1, q = 3 p - 2}, While[PrimeQ[q], q = 3 q - 2; k++]; k]; a[n_] := Block[{p=2}, While[c[p] < n, p = NextPrime[p]]; p]; Array[a, 7]

PROG

(PARI) a(n)={x=1; k=1; while(k==1, m=0; y=x; while(isprime(y), m++; if(m==n, k=x); y=3*y-2); x++); k; }

CROSSREFS

Cf. A083388.

Sequence in context: A154695 A154646 A046826 * A054892 A104570 A071915

Adjacent sequences:  A323710 A323711 A323712 * A323714 A323715 A323716

KEYWORD

nonn,more

AUTHOR

Jinyuan Wang, Jan 25 2019

EXTENSIONS

a(8)-a(11) from Daniel Suteu, Jan 27 2019

a(12)-a(13) from Giovanni Resta, Feb 04 2019

STATUS

approved

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Last modified July 5 21:00 EDT 2020. Contains 335473 sequences. (Running on oeis4.)