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More about 1729 (Posted on 2012-01-04) Difficulty: 3 of 5
Much was said about 1729 a.k.a. Ramanujan number.or a taxicab number.
1729 is also a Carmichael number and the first absolute Euler pseudoprime, a sphenic number, a Zeisel number etc etc

  Please note the following (and solve):
  1. 1729 is one of four positive integers (with the others being A, B and the trivial case 1) which, when its digits are added together, produces a sum which, when multiplied by its reversal, yields the original number:
1 + 7 + 2 + 9 = 19 ; 19*91 = 1729
Find A and B.

2. 1729= xyz, where x,y and z are integer members of an arithmetic progression.
Find these members.

3. 1729 can be expressed (in more than one way) as a sum of distinct Fibonacci numbers
List all the expressions.
 

See The Solution Submitted by Ady TZIDON    
Rating: 5.0000 (3 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re(3): computer solution | Comment 5 of 8 |
(In reply to re(2): computer solution by Daniel)

The revised program below allows for both 1's to be used:

DECLARE SUB addon (wh#)
CLEAR , , 25000
DEFDBL A-Z
DIM SHARED sum
CLS

FOR sum = 2 TO 99999
  s$ = LTRIM$(STR$(sum))
  r$ = ""
  FOR i = 1 TO LEN(s$)
    r$ = MID$(s$, i, 1) + r$
  NEXT
  rev = VAL(r$)
  prod = sum * rev
  p$ = LTRIM$(STR$(prod))
  sum2 = 0
  FOR i = 1 TO LEN(p$)
    sum2 = sum2 + VAL(MID$(p$, i, 1))
  NEXT
  IF sum = sum2 THEN
    PRINT sum; rev; prod
  END IF
NEXT

PRINT : PRINT

part3:
DIM SHARED fib(20), hs(20), sumto(20), solct
fib(0) = 1: fib(1) = 1
FOR i = 2 TO 20
 fib(i) = fib(i - 2) + fib(i - 1)
 IF fib(i) > 1729 THEN EXIT FOR
NEXT: PRINT
maxsub = i - 1

sum = 0: leastStart = 0
FOR i = 0 TO maxsub
  sum = sum + fib(i): sumto(i) = sum
  IF sum > 1729 AND leastStart = 0 THEN leastStart = i - 1
NEXT


FOR st = leastStart TO maxsub
  hs(1) = st: sum = fib(st)
  addon 2
NEXT
PRINT solct

SUB addon (wh)
 newstart = hs(wh - 1) - 1
 FOR try = newstart TO 0 STEP -1
   IF sum + sumto(try) < 1729 THEN EXIT FOR
   hs(wh) = try
   sum = sum + fib(try)
   IF sum = 1729 AND (hs(wh) <> 0 OR hs(wh - 1) = 1) THEN
    FOR i = 1 TO wh
      PRINT fib(hs(i));
    NEXT
    PRINT
    solct = solct + 1
   ELSE
    IF sum < 1729 THEN
     addon wh + 1
    END IF
   END IF
   sum = sum - fib(try)
 NEXT
END SUB

The revised list it finds is:

 987  610  89  34  8  1
 987  610  89  34  5  3  1
 987  610  89  34  5  2  1  1
 987  610  89  21  13  8  1
 987  610  89  21  13  5  3  1
 987  610  89  21  13  5  2  1  1
 987  610  55  34  21  13  8  1
 987  610  55  34  21  13  5  3  1
 987  610  55  34  21  13  5  2  1  1
 987  377  233  89  34  8  1
 987  377  233  89  34  5  3  1
 987  377  233  89  34  5  2  1  1
 987  377  233  89  21  13  8  1
 987  377  233  89  21  13  5  3  1
 987  377  233  89  21  13  5  2  1  1
 987  377  233  55  34  21  13  8  1
 987  377  233  55  34  21  13  5  3  1
 987  377  233  55  34  21  13  5  2  1  1
 987  377  144  89  55  34  21  13  8  1
 987  377  144  89  55  34  21  13  5  3  1
 987  377  144  89  55  34  21  13  5  2  1  1
 1597  89  34  8  1
 1597  89  34  5  3  1
 1597  89  34  5  2  1  1
 1597  89  21  13  8  1
 1597  89  21  13  5  3  1
 1597  89  21  13  5  2  1  1
 1597  55  34  21  13  8  1
 1597  55  34  21  13  5  3  1
 1597  55  34  21  13  5  2  1  1

in agreement with the previous posts.


  Posted by Charlie on 2012-01-04 15:03:09
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