638 is the sum of four consecutive primes: 151 + 157 + 163 + 167 = 638.
638 is the solution to the postage stamp problem for 7 denominations and 6 stamps.
638 is a centered heptagonal number.
The Islamic calendar was introduced in the year 638.
Source: Wikipedia
638 is a centered heptagonal number.
The Islamic calendar was introduced in the year 638.
Source: Wikipedia
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