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Geo Pyramid (Posted on 2008-12-16) Difficulty: 3 of 5
A figurate number stack is built using only the digits 0 through 9 exactly once.

Each tier is a figurate number of the order labelled; no number has a leading zero.


How many solutions can you offer?

See The Solution Submitted by brianjn    
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Solution computer solution | Comment 1 of 4

The program below originally produced the following table in 2-digit triangle order, but I re-sorted it to be in order of the "unit" number.

I'm not sure what counts as a valid unit number, but what is shown is what is left after the triangular, square and pentagonal numbers use up all but one of the ten digits.


1 78 324 9560
2 45 361 9087
2 91 784 6305
3 15 784 6902
3 21 784 9560
4 10 529 3876
4 28 169 5370
4 28 196 5370
4 28 961 5370
4 36 289 5017
4 78 169 2035
4 78 196 2035
4 78 961 2035
4 91 576 2380
6 15 324 9087
6 15 784 3290
6 91 784 2035
7 36 289 4510
7 45 169 2380
7 45 196 2380
7 45 961 2380
8 36 729 4510
9 21 784 6305
9 36 784 1520
9 36 784 2501
9 78 324 6501

DIM t$(81), s$(81), p$(81)
CLS
FOR n = 1 TO 81
  tri = n * (n + 1) / 2
  tr$ = LTRIM$(STR$(tri))
  sq = n * n
  sq$ = LTRIM$(STR$(sq))
  pent = n * (3 * n - 1) / 2
  pe$ = LTRIM$(STR$(pent))
  IF LEN(tr$) = 1 THEN COLOR 12: PRINT tr$; " "; : COLOR 7
  IF LEN(sq$) = 1 THEN COLOR 14: PRINT sq$; " "; : COLOR 7
  IF LEN(pe$) = 1 THEN COLOR 10: PRINT pe$; " "; : COLOR 7

  IF LEN(tr$) = 2 THEN
      good = 1
      FOR i = 1 TO LEN(tr$) - 1
        IF INSTR(i + 1, tr$, MID$(tr$, i, 1)) THEN good = 0: EXIT FOR
      NEXT
      IF good THEN
        tCt = tCt + 1
        t$(tCt) = tr$
      END IF
  END IF
  IF LEN(sq$) = 3 THEN
      good = 1
      FOR i = 1 TO LEN(sq$) - 1
        IF INSTR(i + 1, sq$, MID$(sq$, i, 1)) THEN good = 0: EXIT FOR
      NEXT
      IF good THEN
        sCt = sCt + 1
        s$(sCt) = sq$
      END IF
  END IF
  IF LEN(pe$) = 4 THEN
      good = 1
      FOR i = 1 TO LEN(pe$) - 1
        IF INSTR(i + 1, pe$, MID$(pe$, i, 1)) THEN good = 0: EXIT FOR
      NEXT
      IF good THEN
        pCt = pCt + 1
        p$(pCt) = pe$
      END IF
  END IF
NEXT
PRINT
FOR i = 1 TO tCt: PRINT t$(i); " "; : NEXT: PRINT
FOR i = 1 TO sCt: PRINT s$(i); " "; : NEXT: PRINT
FOR i = 1 TO pCt: PRINT p$(i); " "; : NEXT: PRINT

PRINT

FOR i = 1 TO tCt
 FOR j = 1 TO sCt
  FOR k = 1 TO pCt
    o$ = t$(i) + s$(j) + p$(k)
    good = 1
    FOR l = 1 TO LEN(o$) - 1
      IF INSTR(l + 1, o$, MID$(o$, l, 1)) THEN good = 0: EXIT FOR
    NEXT
    miss = 0
    IF good THEN
      FOR l = 1 TO 9
        IF INSTR(o$, LTRIM$(STR$(l))) = 0 THEN miss = l
      NEXT
      IF miss > 0 THEN
       PRINT miss; t$(i); " "; s$(j); " "; p$(k)
      END IF
    END IF
  NEXT
 NEXT
NEXT

The program also lists what the valid triangular, square and pentagonal numbers in the given ranges are:

10 15 21 28 36 45 78 91

169 196 256 289 324 361 529 576 625 729 784 841 961

1247 1426 1520 1820 1926 2035 2147 2380 2501 3015 3290 3725 3876 4187 4510 5017 5192 5370 6305 6501 6902 7315 7526 9087 9560 9801


  Posted by Charlie on 2008-12-16 17:53:55
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