A086409 a[1]=1; a[n+1]=a[n]-1 if (prime[a[n]]+1)/2 is even, else a[n+1]=a[n]+4.

1, 5, 4, 3, 7, 11, 10, 14, 13, 17, 16, 20, 19, 18, 22, 21, 25, 29, 33, 37, 41, 40, 44, 48, 47, 46, 45, 49, 48, 47, 46, 45, 49, 48, 47, 46, 45, 49, 48, 47, 46, 45, 49, 48, 47, 46, 45, 49, 48, 47, 46

Offset

1,2

Comments

There is a cycle starting with a(26)=46: ...46,45,49,48,47,46,...

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

a(3)=4 because a(2)=5, prime[5]=11 (11+1)/2 is even and a(3)=a(2)-1

Mathematica

b=1; Prepend[Table[b+=If[EvenQ[(Prime[b]+1)/2], -1, 4], {i, 52}], 1] (*A086409*)
NestList[If[EvenQ[(Prime[#]+1)/2], #-1, #+4]&, 1, 50] (* Harvey P. Dale, Mar 05 2020 *)

Crossrefs

Cf. A086407, A086408.

Sequence in context: A256099 A192918 A092156 * A202412 A194556 A154198

Adjacent sequences: A086406 A086407 A086408 * A086410 A086411 A086412

Keyword

easy,nonn

Author

Zak Seidov, Jul 18 2003

Status

approved