Harshad number
= Harshad number
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= Harshad
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A Harshad number in base $b\ge2$ is a <positive integer> divisible by its <base-p digit sum> in that base. In base ten, $18$ is a Harshad number because $1+8=9$ divides $18$. It is strong when the quotient by its <base-p digit sum> is <prime>, and right-truncatable when every nonempty prefix is a Harshad number.