Step 2: Calculate the sum of digits of a 1 to get n2, and calculate n2? +1 a2a 2 =(65)
Step 3: Calculate the sum of digits of a2 to get n3, and then calculate n3? A3a3 of+1 = (112)
......
And so on, a20 12=(65)
Analysis:
Judging from the meaning of the question:
n 1=4+ 1=5,a 1 = 5×5+ 1 = 26;
n2=2+6=8,a2 = 8×8+ 1 = 65;
n3=6+5= 1 1,a3 = 1 1× 1 1+ 1 = 122;
n4= 1+2+2=5,a4 = 5×5+ 1 = 26;
…
Three-number cycle
∴n20 12 is the second in the 672nd cycle.
∴a20 12=a 1=65.