21811957 has 2 divisors, whose sum is σ = 21811958. Its totient is φ = 21811956.

The previous prime is 21811939. The next prime is 21811987. The reversal of 21811957 is 75911812.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21771556 + 40401 = 4666^2 + 201^2 .

It is a cyclic number.

It is not a de Polignac number, because 21811957 - 2²³ = 13423349 is a prime.

It is a super-2 number, since 2×21811957² = 951522936339698, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21811927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10905978 + 10905979.

It is an arithmetic number, because the mean of its divisors is an integer number (10905979).

Almost surely, 2^21811957 is an apocalyptic number.

It is an amenable number.

21811957 is a deficient number, since it is larger than the sum of its proper divisors (1).

21811957 is an equidigital number, since it uses as much as digits as its factorization.

21811957 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5040, while the sum is 34.

The square root of 21811957 is about 4670.3272904583. The cubic root of 21811957 is about 279.4033084104.

The spelling of 21811957 in words is "twenty-one million, eight hundred eleven thousand, nine hundred fifty-seven".