This is a Fibonacci sequence where the first two terms are known as 'seed values' and successive terms are the sum of the two previous terms.
4 = 3 + 1
7 = 4 + 3
11 = 7 + 4
18 = 11 + 7.
Add 3 each time
1+3=4 3+4=7 4+7=11 7+11=18 11+18=29 18+29=47
3 4 6 9 13 18...1....2....3....4......5
19 + 3 = 22 to repeat the pattern
(11/18) - (1/6) = (11/18) - (3/18) = (11-3)/18 = 8/18 = 4/9
Add 3 each time
1+3=4 3+4=7 4+7=11 7+11=18 11+18=29 18+29=47
1, 3, 4, 7, 11, 18, 29, 47
With each new term, you add a number n. This number is always odd, and increases by 2 with each term. So, starting with the first term, 2, you add n = 1 to get 3; add 3 to n = 3 to get 6; add 6 to 5 to get 11; and 7 to 11 to get 18. Here is the pattern written out: 2 + 1 = 3 3 + 3 = 6 6 + 5 = 11 11 + 7 = 18 ...
3 4 6 9 13 18...1....2....3....4......5
19 + 3 = 22 to repeat the pattern
(11/18) - (1/6) = (11/18) - (3/18) = (11-3)/18 = 8/18 = 4/9
The GCF is 1.
11/18 - 1/6 = 11/18 - 3/18 = 8/18 = 4/9
t(n) = 3(-n2 + 6n - 2) for n = 1, 2, 3 etc
There are many possibilities. One is: Un = (8n3 - 39n2 + 79n - 36)/6 for n = 1, 2, 3, ...
The rule for the nth term is t(0) = 23 t(n) = mod[t(n-1) + 2n-1, 26] for n = 1, 2, 3, ...