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A352603 a(1) = 2; a(2) = 3; for n >= 3, a(n) = a(n-1) - (gpf(n-2) + gpf(n-1)) if a(n) >= 2 and has not previously appeared, otherwise a(n) = a(n-1) + (gpf(n-2) + gpf(n-1)), where gpf(k) = A006530(k) = greatest prime dividing k. 1

%I

%S 2,3,8,13,28,48,38,16,37,76,20,44,60,76,52,84,64,55,42,24,14,4,13,28,

%T 48,58,26,68,98,74,30,72,80,88,104,128,113,228,96,118,56,122,54,118,

%U 180,116,82,12,56,46,76,34,70,94,40,92,120,148,106,196,136,112,136,160,138,110,144,130,114

%N a(1) = 2; a(2) = 3; for n >= 3, a(n) = a(n-1) - (gpf(n-2) + gpf(n-1)) if a(n) >= 2 and has not previously appeared, otherwise a(n) = a(n-1) + (gpf(n-2) + gpf(n-1)), where gpf(k) = A006530(k) = greatest prime dividing k.

%C This sequence uses a similar rule to the Recaman sequence A005132 except that here the step size is set to be the sum of the greatest primes dividing the previous two terms.

%C In the first 100000 terms many small numbers do not appear, e.g., 5, 6, 7, 9. It is unknown if these eventually appear. In the same range numerous numbers appear multiple times, e.g., 47964 appears six times. The largest term in the range is a(98963) = 1529048.

%H Scott R. Shannon, <a href="/A352603/a352603.png">Line graph of the first 100000 terms</a>.

%e a(3) = 8 as gpf(2) + gpf(3) = 2 + 3 = 5, so a(3) = a(2) + 5 = 8.

%e a(4) = 13 as gpf(3) + gpf(8) = 3 + 2 = 5, and as 8 - 5 = 3 has already appeared, a(4) = a(3) + 5 = 13.

%e a(7) = 38 as gpf(28) + gpf(48) = 7 + 3 = 10, and as 48 - 10 = 38 has not appeared, a(7) = 38.

%Y Cf. A006530, A005132, A000040.

%K nonn

%O 1,1

%A _Scott R. Shannon_, Mar 22 2022

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Last modified August 17 15:14 EDT 2022. Contains 356189 sequences. (Running on oeis4.)