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A177904 a(1)=a(2)=a(3)=1; thereafter a(n) = gpf(a(n-1)+a(n-2)+a(n-3)), where gpf = "greatest prime factor". 9
1, 1, 1, 3, 5, 3, 11, 19, 11, 41, 71, 41, 17, 43, 101, 23, 167, 97, 41, 61, 199, 43, 101, 7, 151, 37, 13, 67, 13, 31, 37, 3, 71, 37, 37, 29, 103, 13, 29, 29, 71, 43, 13, 127, 61, 67, 17, 29, 113, 53, 13, 179, 7, 199, 11, 31, 241, 283, 37, 17, 337, 23, 29, 389, 7, 17, 59, 83, 53, 13, 149, 43, 41, 233, 317, 197, 83, 199, 479, 761, 1439, 47, 107 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

After 86 steps, enters a cycle of length 212 (see A177923).

LINKS

N. J. A. Sloane, Table of n, a(n) for n = 1..1000

G. Back and M. Caragiu, The greatest prime factor and recurrent sequences, Fib. Q., 48 (2010), 358-362.

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;

M:=1000;

t1:=[1, 1, 1];

for n from 4 to M do

t1:=[op(t1), A006530(t1[n-1]+t1[n-2]+t1[n-3])]; od:

t1;

PROG

(Haskell)

a177904 n = a177904_list !! (n-1)

a177904_list = 1 : 1 : 1 : (map a006530 $ zipWith (+)

   a177904_list (tail $ zipWith (+) a177904_list $ tail a177904_list))

-- Reinhard Zumkeller, Jul 24 2012

CROSSREFS

Cf. A006530, A175723, A178174, A178095, A214320.

Sequence in context: A089730 A105445 A178095 * A049072 A059887 A023585

Adjacent sequences:  A177901 A177902 A177903 * A177905 A177906 A177907

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Dec 16 2010

STATUS

approved

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Last modified March 29 21:48 EDT 2017. Contains 284288 sequences.