20720421 has 8 divisors (see below), whose sum is σ = 30696960. Its totient is φ = 13813596.

The previous prime is 20720417. The next prime is 20720423. The reversal of 20720421 is 12402702.

It is not a de Polignac number, because 20720421 - 2² = 20720417 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 20720394 and 20720403.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20720423) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 383685 + ... + 383738.

It is an arithmetic number, because the mean of its divisors is an integer number (3837120).

Almost surely, 2^20720421 is an apocalyptic number.

It is an amenable number.

20720421 is a deficient number, since it is larger than the sum of its proper divisors (9976539).

20720421 is an equidigital number, since it uses as much as digits as its factorization.

20720421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 767432 (or 767426 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 18.

The square root of 20720421 is about 4551.9689146566. The cubic root of 20720421 is about 274.6625988796.

The spelling of 20720421 in words is "twenty million, seven hundred twenty thousand, four hundred twenty-one".