A031441 - OEIS

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A031441

a(0) = 3; for n > 0, a(n) is the greatest prime factor of PreviousPrime(a(n-1))*a(n-1)-1 where PreviousPrime(prime(k))=prime(k-1).

3, 5, 7, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23

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OFFSET

0,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 0..1000

EXAMPLE

To get a(3) we compute PreviousPrime(7)=5, 5*7-1=34, greatest prime factor of 34 is 17, so a(3)=17.

MATHEMATICA

a[0] = 3; a[n_] := a[n] = FactorInteger[ NextPrime[ a[n-1], -1]*a[n-1] - 1][[-1, 1]]; Table[a[n], {n, 0, 66}] (* Jean-François Alcover, Mar 09 2012 *)

NestList[FactorInteger[NextPrime[#, -1]*#-1][[-1, 1]]&, 3, 70] (* Harvey P. Dale, Dec 13 2012 *)

CROSSREFS

Cf. A034970, A031442.

Sequence in context: A078683 A099863 A112092 * A078150 A276044 A114265

Adjacent sequences: A031438 A031439 A031440 * A031442 A031443 A031444

KEYWORD

nonn,easy,nice

AUTHOR

Yasutoshi Kohmoto

EXTENSIONS

More terms from James A. Sellers

STATUS

approved