21315491 has 2 divisors, whose sum is σ = 21315492. Its totient is φ = 21315490.

The previous prime is 21315451. The next prime is 21315509. The reversal of 21315491 is 19451312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21315491 - 2²² = 17121187 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21315491.

It is not a weakly prime, because it can be changed into another prime (21315421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10657745 + 10657746.

It is an arithmetic number, because the mean of its divisors is an integer number (10657746).

Almost surely, 2^21315491 is an apocalyptic number.

21315491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21315491 is an equidigital number, since it uses as much as digits as its factorization.

21315491 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1080, while the sum is 26.

The square root of 21315491 is about 4616.8702602521. The cubic root of 21315491 is about 277.2671682809.

The spelling of 21315491 in words is "twenty-one million, three hundred fifteen thousand, four hundred ninety-one".