1721021021 has 2 divisors, whose sum is σ = 1721021022. Its totient is φ = 1721021020.

The previous prime is 1721020991. The next prime is 1721021033. The reversal of 1721021021 is 1201201271.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 922336900 + 798684121 = 30370^2 + 28261^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1721021021 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1721021321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 860510510 + 860510511.

It is an arithmetic number, because the mean of its divisors is an integer number (860510511).

Almost surely, 2^1721021021 is an apocalyptic number.

It is an amenable number.

1721021021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1721021021 is an equidigital number, since it uses as much as digits as its factorization.

1721021021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 56, while the sum is 17.

The square root of 1721021021 is about 41485.1903816290. The cubic root of 1721021021 is about 1198.3823158301.

Adding to 1721021021 its reverse (1201201271), we get a palindrome (2922222292).

The spelling of 1721021021 in words is "one billion, seven hundred twenty-one million, twenty-one thousand, twenty-one".