21951988621 has 2 divisors, whose sum is σ = 21951988622. Its totient is φ = 21951988620.

The previous prime is 21951988571. The next prime is 21951988627. The reversal of 21951988621 is 12688915912.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16303714596 + 5648274025 = 127686^2 + 75155^2 .

It is a cyclic number.

It is not a de Polignac number, because 21951988621 - 2¹⁷ = 21951857549 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21951988627) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10975994310 + 10975994311.

It is an arithmetic number, because the mean of its divisors is an integer number (10975994311).

Almost surely, 2^21951988621 is an apocalyptic number.

It is an amenable number.

21951988621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21951988621 is an equidigital number, since it uses as much as digits as its factorization.

21951988621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 622080, while the sum is 52.

The spelling of 21951988621 in words is "twenty-one billion, nine hundred fifty-one million, nine hundred eighty-eight thousand, six hundred twenty-one".