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 A177923 a(1)=19, a(2)=13, a(3)=37; thereafter a(n) = gpf(a(n-1)+a(n-2)+a(n-3)), where gpf = "greatest prime factor". 3
 19, 13, 37, 23, 73, 19, 23, 23, 13, 59, 19, 13, 13, 5, 31, 7, 43, 3, 53, 11, 67, 131, 19, 31, 181, 11, 223, 83, 317, 89, 163, 569, 821, 1553, 109, 191, 109, 409, 709, 409, 509, 1627, 509, 23, 127, 659, 809, 29, 499, 191, 719, 1409, 773, 967, 67, 139, 23, 229, 23, 11, 263, 11, 19, 293, 19, 331, 643, 331, 29, 59, 419, 13, 491, 71, 23, 13, 107, 13, 19, 139, 19, 59, 31, 109, 199, 113, 421, 733, 181, 89, 59, 47, 13, 17, 11, 41, 23, 5, 23, 17, 5, 5, 3, 13, 7, 23, 43, 73, 139, 17, 229, 11, 257, 71, 113, 7, 191, 311, 509, 337 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This is the periodic part of A177904 - it is periodic with period 212. A smaller start is a(1)=3, a(2)=13, a(3)=7, but that would not produce the terms in the order of their first appearance in A177904. There are several open questions concerning this class of sequences - see the Back-Caragiu reference in A177904. LINKS N. J. A. Sloane, Table of n, a(n) for n = 1..212 MATHEMATICA nxt[{a_, b_, c_}]:={b, c, FactorInteger[a+b+c][[-1, 1]]}; NestList[nxt, {19, 13, 37}, 120][[All, 1]] (* Harvey P. Dale, Dec 11 2018 *) CROSSREFS Cf. A006530, A177904, A175723. Sequence in context: A196188 A089294 A088934 * A155848 A088399 A106706 Adjacent sequences:  A177920 A177921 A177922 * A177924 A177925 A177926 KEYWORD nonn AUTHOR N. J. A. Sloane, Dec 18 2010 STATUS approved

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Last modified November 29 18:41 EST 2021. Contains 349416 sequences. (Running on oeis4.)