A059688 - OEIS

A059688

Length of Cunningham chain containing prime(n) either as initial, internal or final term.

5, 2, 5, 2, 5, 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

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OFFSET

1,1

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

Table of n, a(n) for n=1..105.

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

EXTENSIONS

Offset and a(5) corrected by Sean A. Irvine, Oct 01 2022

STATUS

approved