21510997 has 2 divisors, whose sum is σ = 21510998. Its totient is φ = 21510996.

The previous prime is 21510991. The next prime is 21511013. The reversal of 21510997 is 79901512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17859076 + 3651921 = 4226^2 + 1911^2 .

It is a cyclic number.

It is not a de Polignac number, because 21510997 - 2¹⁵ = 21478229 is a prime.

It is a congruent number.

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

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10755498 + 10755499.

It is an arithmetic number, because the mean of its divisors is an integer number (10755499).

Almost surely, 2^21510997 is an apocalyptic number.

It is an amenable number.

21510997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21510997 is an equidigital number, since it uses as much as digits as its factorization.

21510997 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5670, while the sum is 34.

The square root of 21510997 is about 4637.9949331581. The cubic root of 21510997 is about 278.1122892310.

The spelling of 21510997 in words is "twenty-one million, five hundred ten thousand, nine hundred ninety-seven".