20487721 has 2 divisors, whose sum is σ = 20487722. Its totient is φ = 20487720.

The previous prime is 20487713. The next prime is 20487739. The reversal of 20487721 is 12778402.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17943696 + 2544025 = 4236^2 + 1595^2 .

It is a cyclic number.

It is not a de Polignac number, because 20487721 - 2³ = 20487713 is a prime.

It is not a weakly prime, because it can be changed into another prime (20487821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10243860 + 10243861.

It is an arithmetic number, because the mean of its divisors is an integer number (10243861).

Almost surely, 2^20487721 is an apocalyptic number.

It is an amenable number.

20487721 is a deficient number, since it is larger than the sum of its proper divisors (1).

20487721 is an equidigital number, since it uses as much as digits as its factorization.

20487721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6272, while the sum is 31.

The square root of 20487721 is about 4526.3363772482. The cubic root of 20487721 is about 273.6305292430.

The spelling of 20487721 in words is "twenty million, four hundred eighty-seven thousand, seven hundred twenty-one".