搜狐畅游——数列计算

#encoding=utf-8

import sys
import math

n,k=map( lambda x:int(x),sys.stdin.readline().strip("\n").split(" ") )

if k==1:
    print 1
    exit(0)
elif k==2:
    print pow( n,1 )
    exit( 0 )

root = int( math.log( k,2 ) )

# print root

res=[None]*pow( 2,root )
res.append( 0 )

for i in range( root+1 ):
    res[ pow( 2,i ) ]=pow( n,i )

# print res

for i in range( 1,root ):
    pre=1
    post=pow( 2,i )

    start=pow( 2,i )+1
    end=pow( 2,i+1 )

    # print pre,post,start,end

    count=0
    for j in range( pre,post ):
        res[ start+count ]=res[j]+res[post]
        count+=1

res=res[1:]
# print len( res )

count=0
while True:
    if len(res)!=k:
        res.append(res[count] + res[pow(2, root) - 1])
        count+=1
    else:
        print res[-1]
        break