21656513 has 2 divisors, whose sum is σ = 21656514. Its totient is φ = 21656512.

The previous prime is 21656461. The next prime is 21656539. The reversal of 21656513 is 31565612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14077504 + 7579009 = 3752^2 + 2753^2 .

It is a cyclic number.

It is not a de Polignac number, because 21656513 - 2⁶ = 21656449 is a prime.

It is not a weakly prime, because it can be changed into another prime (21656543) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10828256 + 10828257.

It is an arithmetic number, because the mean of its divisors is an integer number (10828257).

Almost surely, 2^21656513 is an apocalyptic number.

It is an amenable number.

21656513 is a deficient number, since it is larger than the sum of its proper divisors (1).

21656513 is an equidigital number, since it uses as much as digits as its factorization.

21656513 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5400, while the sum is 29.

The square root of 21656513 is about 4653.6558746861. The cubic root of 21656513 is about 278.7379982365.

Subtracting 21656513 from its reverse (31565612), we obtain a palindrome (9909099).

The spelling of 21656513 in words is "twenty-one million, six hundred fifty-six thousand, five hundred thirteen".