21510961 has 2 divisors, whose sum is σ = 21510962. Its totient is φ = 21510960.

The previous prime is 21510943. The next prime is 21510977. The reversal of 21510961 is 16901512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18870336 + 2640625 = 4344^2 + 1625^2 .

It is a cyclic number.

It is not a de Polignac number, because 21510961 - 2⁷ = 21510833 is a prime.

It is not a weakly prime, because it can be changed into another prime (21510991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10755480 + 10755481.

It is an arithmetic number, because the mean of its divisors is an integer number (10755481).

Almost surely, 2^21510961 is an apocalyptic number.

It is an amenable number.

21510961 is a deficient number, since it is larger than the sum of its proper divisors (1).

21510961 is an equidigital number, since it uses as much as digits as its factorization.

21510961 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 540, while the sum is 25.

The square root of 21510961 is about 4637.9910521690. The cubic root of 21510961 is about 278.1121340848.

The spelling of 21510961 in words is "twenty-one million, five hundred ten thousand, nine hundred sixty-one".