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A214320 a(0)=a(1)=a(2)=1; thereafter a(n) = gpf(a(n-1)+a(n-3)), where gpf = "greatest prime factor". 3
1, 1, 1, 2, 3, 2, 2, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3, 5, 2, 5, 5, 7, 3, 2, 3, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Suggested by A214551 and A177904.

LINKS

Table of n, a(n) for n=0..120.

FORMULA

After 7 terms, cycles with period 9.

MAPLE

with(numtheory, divisors); A006530 := proc(n) local i, t1, t2, t3, t4, t5; t1 := divisors(n); t2 := convert(t1, list); t3 := sort(t2); t4 := nops(t3); t5 := 1; for i from 1 to t4 do if isprime(t3[t4+1-i]) then RETURN(t3[t4+1-i]); fi; od; 1; end;

f:=proc(n) option remember; if n <= 2 then 1 else A006530(f(n-1)+f(n-3)); fi; end;

[seq(f(n), n=0..120)];

MATHEMATICA

nxt[{a_, b_, c_}]:={b, c, FactorInteger[c+a][[-1, 1]]}; NestList[nxt, {1, 1, 1}, 120][[All, 1]] (* or *) PadRight[{1, 1, 1, 2, 3, 2, 2}, 130, {3, 2, 3, 3, 5, 2, 5, 5, 7}] (* Harvey P. Dale, Jul 08 2017 *)

PROG

(Haskell)

a214320 n = a214320_list !! n

a214320_list = 1 : 1 : 1 : (map a006530 $

   zipWith (+) a214320_list (drop 2 $ a214320_list))

-- Reinhard Zumkeller, Jul 24 2012

CROSSREFS

Cf. A000930, A006530, A177904, A214320.

Sequence in context: A318177 A128651 A093797 * A119809 A007653 A272181

Adjacent sequences:  A214317 A214318 A214319 * A214321 A214322 A214323

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jul 22 2012

STATUS

approved

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Last modified September 24 05:29 EDT 2021. Contains 347623 sequences. (Running on oeis4.)