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A129741 List of primitive prime divisors of the Somos-4 sequence (A006720) in their order of occurrence. 4
2, 3, 7, 23, 59, 157, 11, 139, 8209, 9257, 620297, 983, 4003, 1847, 9803, 1687054711, 1433, 33008447, 83, 101, 113, 51563, 61, 823, 5381, 20117, 6329, 262650531833, 197, 10259, 519606349, 2621, 11887, 136667817691, 13933, 42591667, 564188663, 211, 8802371 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Read A006720 term-by-term, factorize each term, write down any primes not seen before.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..121 (from the first 49 terms)

G. Everest et al., Primes generated by recurrence sequences, Amer. Math. Monthly, 114 (No. 5, 2007), 417-431.

MATHEMATICA

a[0] = a[1] = a[2] = a[3] = 1; a[n_] := a[n] = (a[n - 1] a[n - 3] + a[n - 2]^2)/a[n - 4]; t = Array[a, 30]; t2 = {}; ps = {}; Do[f = Transpose[FactorInteger[t[[n]]]][[1]]; c = Complement[f, ps]; t2 = Join[t2, c]; ps = Union[ps, c], {n, 4, 30}]; t2 (* T. D. Noe, Nov 19 2013 *)

CROSSREFS

Cf. A006720, A129739, A129740.

Cf. A227199 (primes in this sequence).

Sequence in context: A037231 A248525 A082449 * A006720 A084710 A088173

Adjacent sequences:  A129738 A129739 A129740 * A129742 A129743 A129744

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, May 13 2007

EXTENSIONS

Order of some of the terms corrected by T. D. Noe, Nov 19 2013

STATUS

approved

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Last modified January 17 09:32 EST 2020. Contains 330949 sequences. (Running on oeis4.)