1645249621 has 2 divisors, whose sum is σ = 1645249622. Its totient is φ = 1645249620.

The previous prime is 1645249609. The next prime is 1645249657. The reversal of 1645249621 is 1269425461.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1266363396 + 378886225 = 35586^2 + 19465^2 .

It is a cyclic number.

It is not a de Polignac number, because 1645249621 - 2¹⁷ = 1645118549 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1645249601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 822624810 + 822624811.

It is an arithmetic number, because the mean of its divisors is an integer number (822624811).

Almost surely, 2^1645249621 is an apocalyptic number.

It is an amenable number.

1645249621 is a deficient number, since it is larger than the sum of its proper divisors (1).

1645249621 is an equidigital number, since it uses as much as digits as its factorization.

1645249621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 103680, while the sum is 40.

The square root of 1645249621 is about 40561.6767528168. The cubic root of 1645249621 is about 1180.5306482884.

The spelling of 1645249621 in words is "one billion, six hundred forty-five million, two hundred forty-nine thousand, six hundred twenty-one".