20991690 has 32 divisors (see below), whose sum is σ = 55978560. Its totient is φ = 5597712.

The previous prime is 20991653. The next prime is 20991721. The reversal of 20991690 is 9619902.

It is a super-2 number, since 2×20991690² = 881302098112200, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 38604 + ... + 39143.

It is an arithmetic number, because the mean of its divisors is an integer number (1749330).

Almost surely, 2^20991690 is an apocalyptic number.

20991690 is an abundant number, since it is smaller than the sum of its proper divisors (34986870).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20991690 is a wasteful number, since it uses less digits than its factorization.

20991690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77763 (or 77757 counting only the distinct ones).

The product of its (nonzero) digits is 8748, while the sum is 36.

The square root of 20991690 is about 4581.6689099061. The cubic root of 20991690 is about 275.8560213132.

The spelling of 20991690 in words is "twenty million, nine hundred ninety-one thousand, six hundred ninety".