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 A059688 Length of Cunningham chain containing prime(n) either as initial, internal or final term. 2
 5, 2, 5, 2, 2, 0, 0, 0, 5, 2, 0, 0, 3, 0, 5, 2, 2, 0, 0, 0, 0, 0, 3, 6, 0, 0, 0, 2, 0, 2, 0, 2, 0, 0, 0, 0, 0, 0, 3, 2, 6, 0, 2, 0, 0, 0, 0, 0, 2, 0, 2, 2, 0, 2, 0, 2, 0, 0, 0, 2, 0, 2, 0, 0, 0, 0, 0, 0, 2, 0, 0, 6, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 2, 0, 0, 2, 0, 0, 0, 0, 2, 2, 0, 2, 0, 2, 4, 0, 0, 0, 0, 0, 2, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS The length of a chain is measured by the total number of terms including the end points. a(n)=0 means that prime(n) is neither Sophie Germain nor a safe prime (i.e. it is in A059500). LINKS C. K. Caldwell, Cunningham Chains W. Roonguthai, Yves Gallot's Proth.exe and Cunningham Chains EXAMPLE For all of {2,5,11,23,47}, i.e. at positions {j}={1,3,5,9,15} a(j)=5. Similarly for indices of all terms in {89,...,5759} a(i)=6. No chains are intelligible with length = 1 because the minimal chain enclose one Sophie Germain and also one safe prime. Dominant values are 0 and 2. CROSSREFS Cf. A005384, A005385, A053176, A059452-A059456, A007700, A005602, A023272, A023302, A023330, A059500. Sequence in context: A008566 A111129 A168464 * A072996 A244892 A278066 Adjacent sequences:  A059685 A059686 A059687 * A059689 A059690 A059691 KEYWORD nonn AUTHOR Labos Elemer, Feb 06 2001 STATUS approved

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Last modified July 27 15:49 EDT 2021. Contains 346308 sequences. (Running on oeis4.)