A086407 a[1]=1; a[n+1]=a[n]-1 if mod[prime[a[n]],6]=5, else a[n+1]=a[n]+4.

1, 5, 4, 8, 12, 16, 15, 14, 18, 22, 26, 25, 29, 33, 32, 31, 35, 34, 38, 42, 46, 50, 54, 53, 57, 56, 55, 54, 53, 57, 56, 55, 54, 53, 57, 56, 55, 54, 53, 57, 56, 55, 54, 53, 57, 56, 55, 54, 53, 57, 56, 55, 54

Offset

1,2

Comments

There is a cycle ...54,53,57,56,55,54,...

Links

Table of n, a(n) for n=1..53.

Example

a(3)=4 because a(2)=5, prime[5]=11=1 (mod 6) and a(3)=a(2)-1

Mathematica

b=1; Prepend[Table[b+=If[Mod[Prime[b], 6]\[Equal]5, -1, 4], {i, 32}], 1]
nxt[a_]:=If[Mod[Prime[a], 6]==5, a-1, a+4]; NestList[nxt, 1, 60] (* Harvey P. Dale, May 29 2013 *)

Crossrefs

Cf. A086408, A086409.

Sequence in context: A388215 A309543 A187891 * A160427 A343244 A215337

Adjacent sequences: A086404 A086405 A086406 * A086408 A086409 A086410

Keyword

easy,nonn

Author

Zak Seidov, Jul 18 2003

Status

approved