3 7 15 ? 63
R. 31
3 7 15 ? 63
R. 31
3+4 = 7 4=2^2
7+8 = 15 8=2^3
15+16 =31 16=2^4
31+32=63 32=2^5
3 7 15 ? 63 R. 31
7 = 2*3+1
15 = 2*7+1
n = 2*15*1 = 31
63 = 2*31+1
3 7 15 ? 63
R. 31
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$3$;
$3+2^2 = 3+4=7$;
$7+2^3=7+8 = 15$;
$15+2^4 = 15+16 = 31$ ←;
$31+2^5= 31+32 = 63$.