21196561 has 2 divisors, whose sum is σ = 21196562. Its totient is φ = 21196560.

The previous prime is 21196541. The next prime is 21196573. The reversal of 21196561 is 16569112.

21196561 = 3255² + 3256².

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10601536 + 10595025 = 3256^2 + 3255^2 .

It is a cyclic number.

It is not a de Polignac number, because 21196561 - 2¹¹ = 21194513 is a prime.

It is not a weakly prime, because it can be changed into another prime (21196531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10598280 + 10598281.

It is an arithmetic number, because the mean of its divisors is an integer number (10598281).

Almost surely, 2^21196561 is an apocalyptic number.

21196561 is the 3256-th centered square number.

It is an amenable number.

21196561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21196561 is an equidigital number, since it uses as much as digits as its factorization.

21196561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 31.

The square root of 21196561 is about 4603.9723066065. The cubic root of 21196561 is about 276.7505345649.

The spelling of 21196561 in words is "twenty-one million, one hundred ninety-six thousand, five hundred sixty-one".