1621540651 has 4 divisors (see below), whose sum is σ = 1665366112. Its totient is φ = 1577715192.

The previous prime is 1621540637. The next prime is 1621540667. The reversal of 1621540651 is 1560451261.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1560451261 = 23 ⋅67845707.

It is a cyclic number.

It is not a de Polignac number, because 1621540651 - 2¹⁵ = 1621507883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1621540681) 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 in 3 ways as a sum of consecutive naturals, for example, 21912675 + ... + 21912748.

It is an arithmetic number, because the mean of its divisors is an integer number (416341528).

Almost surely, 2^1621540651 is an apocalyptic number.

1621540651 is a deficient number, since it is larger than the sum of its proper divisors (43825461).

1621540651 is an equidigital number, since it uses as much as digits as its factorization.

1621540651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43825460.

The product of its (nonzero) digits is 7200, while the sum is 31.

The square root of 1621540651 is about 40268.3579377158. The cubic root of 1621540651 is about 1174.8324857920.

The spelling of 1621540651 in words is "one billion, six hundred twenty-one million, five hundred forty thousand, six hundred fifty-one".