1921650721 has 2 divisors, whose sum is σ = 1921650722. Its totient is φ = 1921650720.

The previous prime is 1921650719. The next prime is 1921650737. The reversal of 1921650721 is 1270561291.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1465358400 + 456292321 = 38280^2 + 21361^2 .

It is a cyclic number.

It is not a de Polignac number, because 1921650721 - 2¹ = 1921650719 is a prime.

Together with 1921650719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (1921650761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 960825360 + 960825361.

It is an arithmetic number, because the mean of its divisors is an integer number (960825361).

Almost surely, 2^1921650721 is an apocalyptic number.

It is an amenable number.

1921650721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1921650721 is an equidigital number, since it uses as much as digits as its factorization.

1921650721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7560, while the sum is 34.

The square root of 1921650721 is about 43836.6367437102. The cubic root of 1921650721 is about 1243.2490929867.

The spelling of 1921650721 in words is "one billion, nine hundred twenty-one million, six hundred fifty thousand, seven hundred twenty-one".