DigitSum

DigitSum[n] gives the sum of the decimal digits in the integer n.

DigitSum[n,b] gives the sum of the base b digits in the integer n.

DigitSum[n,b,k] gives the sum of the first k base b digits in the integer n.

DigitSum[n,b,-k] gives the sum of the last k base b digits in the integer n.

DigitSum[n,MixedRadix[blist]] uses the mixed radix with list of bases blist.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.