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 A269026 a(1)=1; for n>1, define a sequence {b(m), m >= 1} by b(1)=a(n-1), b(2)=n, and b(m) = A020639(b(m-2)) + A006530(b(m-1)); then a(n) is the number of terms in that sequence before the first of the infinite string of 4s. 1
 1, 9, 12, 1, 4, 10, 5, 6, 8, 6, 5, 3, 15, 7, 12, 2, 17, 7, 4, 6, 13, 11, 8, 10, 9, 3, 12, 9, 11, 3, 12, 2, 16, 6, 12, 10, 5, 11, 12, 6, 9, 7, 12, 14, 13, 11, 16, 10, 5, 7, 12, 14, 8, 10, 5, 11, 4, 10, 17, 15, 15, 7, 8, 2, 5, 3, 15, 7, 4, 9, 12, 10, 5, 10, 13, 3, 11, 11, 11 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Michel Marcus, Table of n, a(n) for n = 1..10000 EXAMPLE n = 3: a(n-1) = a(2) = 9; b(1) = 9, b(2) = 3; the sequence generated is: 9, 3, 6, 6, 5, 7, 12, 10, 7, 9, 10, 8, 4, 4, 4, ... There are 12 terms before the first of the infinite 4s, so a(3) = 12. PROG (PARI) spf(n) = if (n==1, 1, vecmin(factor(n)[, 1])); gpf(n) = if (n==1, 1, vecmax(factor(n)[, 1])); nbt(a, n) = {x = a; y = n; nb = 0; while (!((x==4) && (y==4)), z = spf(x) + gpf(y); x = y; y = z; nb++; ); nb; } lista(nn) = { print1(a=1, ", "); for (n=2, nn, na = nbt(a, n); print1(na, ", "); a = na; ); } \\ Michel Marcus, Apr 12 2016 CROSSREFS Cf. A006530, A020639, A271621. Sequence in context: A159003 A352004 A196509 * A124606 A110647 A347943 Adjacent sequences: A269023 A269024 A269025 * A269027 A269028 A269029 KEYWORD nonn AUTHOR Cody M. Haderlie, Apr 11 2016 STATUS approved

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Last modified May 21 12:09 EDT 2024. Contains 372736 sequences. (Running on oeis4.)