Question

How does 28 become perfect number which greater than 10 but less than 40

Answer 1

Answer:

Of course, it is. It is the second perfect number:

1 + 2 + 4 + 7 + 14 = 28

(just to remind, the 1st perfect number is 6 (1 + 2 + 3 = 6), the 3rd is 496 (1 + 2 + 4 + 8 + 16 + 31 + 62 + 124 + 248 = 496), the 4th is 8128 (1 + 2 + 4 + 8 + 16 + 32 + 64 + 127 + 254 + 508 + 1016 + 2032 + 4064 = 8128), number 5 is 33 550 336 (over 33 million), number 6 is 8 589 869 056 (over 8 billion), number 7 is 137 438 691 328 (over 137 billion), number 8 is 2 305 843 008 139 952 128 (over 2 quintillion), number 9 is 2 658 455 991 569 831 744 654 692 615 953 842 176 (over 658 decillion), number 10 is 191 561 942 608 236 107 294 793 378 084 303 638 130 997 321 548 169 216 (over 191 sexdecellion) etc.)

Isn’t that obvious?

The next perfect number with this property is the 28th perfect number, and its full decimal representation has 51 924 digits.

We can call them bi-perfect numbers (i.e. perfect numbers whose sequence number is a perfect number itself).