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Let f(n) be the solution to this problem if there are n frogs. We have f(1) = 4 and f(2) = 11. Now assume we add one more frog and one more toad. We obtain the recursion

f(n+1) = 2f(n) + 3 - f(n-1).

It is possible to get a closed form equation for f(n), or we can just find f(2), f(3), etc.

f(1) 4
f(2) 11
f(3) 21
f(4) 34
f(5) 50
f(6) 69
f(7) 91
f(8) 116
f(9) 144
f(10) 175
f(11) 209
f(12) 246
f(13) 286
f(14) 329
f(15) 375
f(16) 424
f(17) 476
f(18) 531
f(19) 589
f(20) 650
f(21) 714
f(22) 781
f(23) 851
f(24) 924
f(25) 1000

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