21261071501 has 4 divisors (see below), whose sum is σ = 21261709404. Its totient is φ = 21260433600.

The previous prime is 21261071483. The next prime is 21261071509. The reversal of 21261071501 is 10517016212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 2512615876 + 18748455625 = 50126^2 + 136925^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21261071501 is a prime.

It is a super-2 number, since 2×21261071501² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21261071509) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 266030 + ... + 336591.

It is an arithmetic number, because the mean of its divisors is an integer number (5315427351).

Almost surely, 2^21261071501 is an apocalyptic number.

It is an amenable number.

21261071501 is a deficient number, since it is larger than the sum of its proper divisors (637903).

21261071501 is an equidigital number, since it uses as much as digits as its factorization.

21261071501 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 637902.

The product of its (nonzero) digits is 840, while the sum is 26.

Adding to 21261071501 its reverse (10517016212), we get a palindrome (31778087713).

The spelling of 21261071501 in words is "twenty-one billion, two hundred sixty-one million, seventy-one thousand, five hundred one".