20505990 has 32 divisors (see below), whose sum is σ = 49351680. Its totient is φ = 5453024.

The previous prime is 20505983. The next prime is 20506001. The reversal of 20505990 is 9950502.

20505990 = 244² + 245² + ... + 423².

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

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, 13657 + ... + 15083.

It is an arithmetic number, because the mean of its divisors is an integer number (1542240).

Almost surely, 2^20505990 is an apocalyptic number.

20505990 is an abundant number, since it is smaller than the sum of its proper divisors (28845690).

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

20505990 is a wasteful number, since it uses less digits than its factorization.

20505990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1916.

The product of its (nonzero) digits is 4050, while the sum is 30.

The square root of 20505990 is about 4528.3540055963. The cubic root of 20505990 is about 273.7118376359.

The spelling of 20505990 in words is "twenty million, five hundred five thousand, nine hundred ninety".