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Using only the digits 7, 8 and 9, how many positive seven-digit integers can be made that are palindromes?

Dec 20, 2019

#1
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There are 7*7*7 = 343 palindromes that can be made.

Dec 20, 2019
#2
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a=7;b=7;c=7;d=7;e=7;f=7;g=7;p=0;cycle:n=a*1000000+b*100000+c*10000+d*1000+e*100+f*10+g;if(n<10000000 and a==g and b==f and c==e, goto loop, goto next); loop:printn," ",;p=p+1; next:g++;if(g<10, goto cycle, 0);g=7;f++;if(f<10, goto cycle, 0);g=7;f=7;e++;if(e<10, goto cycle,0);g=7;f=7;e=7;d++;if(d<10, goto cycle,0);g=7;f=7;e=7;d=7;c++;if(c<10, goto cycle,0);g=7;f=7;e=7;d=7;c=7;b++;if(b<10, goto cycle,0);g=7;f=7;e=7;d=7;c=7;b=7;a++;if(a<10, goto cycle,0);print"Total = ",p

OUTPUT: 7777777  7778777  7779777  7787877  7788877  7789877  7797977  7798977  7799977  7877787  7878787  7879787  7887887  7888887  7889887  7897987  7898987  7899987  7977797  7978797  7979797  7987897  7988897  7989897  7997997  7998997  7999997  8777778  8778778  8779778  8787878  8788878  8789878  8797978  8798978  8799978  8877788  8878788  8879788  8887888  8888888  8889888  8897988  8898988  8899988  8977798  8978798  8979798  8987898  8988898  8989898  8997998  8998998  8999998  9777779  9778779  9779779  9787879  9788879  9789879  9797979  9798979  9799979  9877789  9878789  9879789  9887889  9888889  9889889  9897989  9898989  9899989  9977799  9978799  9979799  9987899  9988899  9989899  9997999  9998999  9999999  Total =  81

P.S. There may be a "bug" in the code !! If so, please let me know. Thanks.

Dec 20, 2019