20991663 has 64 divisors (see below), whose sum is σ = 40550400. Its totient is φ = 10406880.

The previous prime is 20991653. The next prime is 20991721. The reversal of 20991663 is 36619902.

It is a de Polignac number, because none of the positive numbers 2^k-20991663 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20991653) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 47598 + ... + 48036.

It is an arithmetic number, because the mean of its divisors is an integer number (633600).

Almost surely, 2^20991663 is an apocalyptic number.

20991663 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

20991663 is the 2898-th heptagonal number.

20991663 is a deficient number, since it is larger than the sum of its proper divisors (19558737).

20991663 is a wasteful number, since it uses less digits than its factorization.

20991663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 489 (or 483 counting only the distinct ones).

The product of its (nonzero) digits is 17496, while the sum is 36.

The square root of 20991663 is about 4581.6659633806. The cubic root of 20991663 is about 275.8559030423.

The spelling of 20991663 in words is "twenty million, nine hundred ninety-one thousand, six hundred sixty-three".