login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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". 10
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;

MATHEMATICA

nxt[{a_, b_, c_}]:={b, c, FactorInteger[a+b+c][[-1, 1]]}; NestList[nxt, {1, 1, 1}, 90][[All, 1]] (* Harvey P. Dale, Jul 17 2017 *)

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: A105445 A328878 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 13 21:06 EDT 2021. Contains 342941 sequences. (Running on oeis4.)