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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. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

LINKS

Table of n, a(n) for n=1..51.

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*)

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

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Last modified October 19 04:40 EDT 2019. Contains 328211 sequences. (Running on oeis4.)