It is a congruent number.
It is an unprimeable number.
Almost surely, 261691220 is an apocalyptic number.
61691220 is a gapful number since it is divisible by the number (60) formed by its first and last digit.
It is an amenable number.
It is a practical number, because each smaller number is the sum of distinct divisors of 61691220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (97909812).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
61691220 is a wasteful number, since it uses less digits than its factorization.
61691220 is an evil number, because the sum of its binary digits is even.
The square root of 61691220 is about 7854.3758504416. The cubic root of 61691220 is about 395.1310145969.
The spelling of 61691220 in words is "sixty-one million, six hundred ninety-one thousand, two hundred twenty".