1021855721 has 2 divisors, whose sum is σ = 1021855722. Its totient is φ = 1021855720.

The previous prime is 1021855711. The next prime is 1021855727. The reversal of 1021855721 is 1275581201.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 606144400 + 415711321 = 24620^2 + 20389^2 .

It is a cyclic number.

It is not a de Polignac number, because 1021855721 - 2¹⁰ = 1021854697 is a prime.

It is a super-2 number, since 2×1021855721² = 2088378229080859682, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1021855727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 510927860 + 510927861.

It is an arithmetic number, because the mean of its divisors is an integer number (510927861).

Almost surely, 2^1021855721 is an apocalyptic number.

It is an amenable number.

1021855721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1021855721 is an equidigital number, since it uses as much as digits as its factorization.

1021855721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5600, while the sum is 32.

The square root of 1021855721 is about 31966.4780825164. The cubic root of 1021855721 is about 1007.2328008017.

The spelling of 1021855721 in words is "one billion, twenty-one million, eight hundred fifty-five thousand, seven hundred twenty-one".