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A121937 a(n) = least m >= 2 such that (n mod m) > (n+2 mod m). 1
3, 3, 4, 3, 3, 4, 3, 3, 5, 3, 3, 7, 3, 3, 4, 3, 3, 4, 3, 3, 11, 3, 3, 5, 3, 3, 4, 3, 3, 4, 3, 3, 5, 3, 3, 19, 3, 3, 4, 3, 3, 4, 3, 3, 23, 3, 3, 5, 3, 3, 4, 3, 3, 4, 3, 3, 29, 3, 3, 31, 3, 3, 4, 3, 3, 4, 3, 3, 5, 3, 3, 37, 3, 3, 4, 3, 3, 4, 3, 3, 41, 3, 3, 5, 3, 3, 4, 3, 3, 4, 3, 3, 5, 3, 3, 7, 3, 3, 4, 3, 3, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

at n = 1,4,7,... and n = 2,5,8,... a(n) = 3; also n = 3,15,27,... and n = 6,18,30,... a(n) = 4; all other terms are apparently primes. In case k=1, for all n, a(n) = least prime divisor of n+1.

LINKS

Table of n, a(n) for n=1..102.

MATHEMATICA

re=Reap[Do[Do[If[Mod[n, k]>Mod[n+2, k], Sow[k]; Break[]], {k, 2, n+2}], {n, 300}]][[2, 1]]

CROSSREFS

Sequence in context: A172515 A188590 A080038 * A003034 A091282 A202708

Adjacent sequences: A121934 A121935 A121936 * A121938 A121939 A121940

KEYWORD

nonn

AUTHOR

Zak Seidov, Sep 03 2006

STATUS

approved

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Last modified January 31 05:28 EST 2023. Contains 359947 sequences. (Running on oeis4.)