28491721 has 2 divisors, whose sum is σ = 28491722. Its totient is φ = 28491720.

The previous prime is 28491709. The next prime is 28491751. The reversal of 28491721 is 12719482.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18020025 + 10471696 = 4245^2 + 3236^2 .

It is a cyclic number.

It is not a de Polignac number, because 28491721 - 2¹⁵ = 28458953 is a prime.

It is not a weakly prime, because it can be changed into another prime (28491751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14245860 + 14245861.

It is an arithmetic number, because the mean of its divisors is an integer number (14245861).

Almost surely, 2^28491721 is an apocalyptic number.

It is an amenable number.

28491721 is a deficient number, since it is larger than the sum of its proper divisors (1).

28491721 is an equidigital number, since it uses as much as digits as its factorization.

28491721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8064, while the sum is 34.

The square root of 28491721 is about 5337.7636703024. The cubic root of 28491721 is about 305.4261569460.

The spelling of 28491721 in words is "twenty-eight million, four hundred ninety-one thousand, seven hundred twenty-one".