21709651 has 2 divisors, whose sum is σ = 21709652. Its totient is φ = 21709650.

The previous prime is 21709621. The next prime is 21709669. The reversal of 21709651 is 15690712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21709651 - 2¹¹ = 21707603 is a prime.

It is not a weakly prime, because it can be changed into another prime (21709601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10854825 + 10854826.

It is an arithmetic number, because the mean of its divisors is an integer number (10854826).

Almost surely, 2^21709651 is an apocalyptic number.

21709651 is a deficient number, since it is larger than the sum of its proper divisors (1).

21709651 is an equidigital number, since it uses as much as digits as its factorization.

21709651 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3780, while the sum is 31.

The square root of 21709651 is about 4659.3616515570. The cubic root of 21709651 is about 278.9657893246.

The spelling of 21709651 in words is "twenty-one million, seven hundred nine thousand, six hundred fifty-one".