The number 70 has some interesting properties.
∙ It’s a pronic number (also called an oblong number)—the product of two consecutive integers: 7 × 10
∙ It’s the sum of the first seven prime numbers: 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19 = 77… wait, let me recalculate that.
Actually, 2 + 3 + 5 + 7 + 11 + 13 + 17 = 58, and adding 19 = 77. So that’s not quite right.
Let me correct myself: 70 is the sum of the first four perfect squares: 1 + 4 + 9 + 16 + 25 + 36 = 91… that’s not it either. I should be more careful here—70 = 1² + 2² + 3² + 4² + 5² + 6² would be 91.
Apologies for the false starts. What is true: 70 is a pentagonal number and a sphenic number (product of three distinct primes: 2 × 5 × 7).
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