1621921979 has 2 divisors, whose sum is σ = 1621921980. Its totient is φ = 1621921978.

The previous prime is 1621921969. The next prime is 1621921999. The reversal of 1621921979 is 9791291261.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1621921979 - 2⁸ = 1621921723 is a prime.

It is not a weakly prime, because it can be changed into another prime (1621921969) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810960989 + 810960990.

It is an arithmetic number, because the mean of its divisors is an integer number (810960990).

Almost surely, 2^1621921979 is an apocalyptic number.

1621921979 is a deficient number, since it is larger than the sum of its proper divisors (1).

1621921979 is an equidigital number, since it uses as much as digits as its factorization.

1621921979 is an evil number, because the sum of its binary digits is even.

The product of its digits is 122472, while the sum is 47.

The square root of 1621921979 is about 40273.0924936241. The cubic root of 1621921979 is about 1174.9245713463.

The spelling of 1621921979 in words is "one billion, six hundred twenty-one million, nine hundred twenty-one thousand, nine hundred seventy-nine".