21511957 has 2 divisors, whose sum is σ = 21511958. Its totient is φ = 21511956.

The previous prime is 21511951. The next prime is 21511967. The reversal of 21511957 is 75911512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19766916 + 1745041 = 4446^2 + 1321^2 .

It is a cyclic number.

It is not a de Polignac number, because 21511957 - 2³ = 21511949 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21511951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10755978 + 10755979.

It is an arithmetic number, because the mean of its divisors is an integer number (10755979).

Almost surely, 2^21511957 is an apocalyptic number.

It is an amenable number.

21511957 is a deficient number, since it is larger than the sum of its proper divisors (1).

21511957 is an equidigital number, since it uses as much as digits as its factorization.

21511957 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3150, while the sum is 31.

The square root of 21511957 is about 4638.0984250013. The cubic root of 21511957 is about 278.1164263990.

The spelling of 21511957 in words is "twenty-one million, five hundred eleven thousand, nine hundred fifty-seven".