Can you identify the five-digit sphenic palindrome
- where the sum of its digits is a palindromic prime,
- where of one its factors is a multi-digit palindromic prime, and
- the sum of its factors is also a palindromic prime?
Can you identify any other sphenic palindrome that has these characteristics?
A sphenic number is a positive integer and product of three distinct primes.
A palindromic number is a number that is the same when written forwards or backwards.
CLS
FOR i = 10000 TO 99999
n$ = LTRIM$(STR$(i))
good = 1
FOR j = 1 TO LEN(n$)
IF MID$(n$, j, 1) <> MID$(n$, LEN(n$) + 1 - j, 1) THEN good = 0: EXIT FOR
NEXT
sod = 0
FOR j = 1 TO 5
sod = sod + VAL(MID$(n$, j, 1))
NEXT
n$ = LTRIM$(STR$(sod))
FOR j = 1 TO LEN(n$)
IF MID$(n$, j, 1) <> MID$(n$, LEN(n$) + 1 - j, 1) THEN good = 0: EXIT FOR
NEXT
factor sod, s$
IF n$ <> LTRIM$(s$) THEN good = 0
IF good THEN
factor i, s$
s$ = LTRIM$(RTRIM$(s$))
ix = INSTR(s$, " ")
IF ix THEN
ix2 = INSTR(ix + 1, s$, " ")
IF ix2 THEN
ix3 = INSTR(ix2 + 1, s$, " ")
IF ix3 = 0 THEN
f1 = VAL(LEFT$(s$, ix - 1))
f2 = VAL(MID$(s$, ix + 1, ix2 - ix - 1))
f3 = VAL(MID$(s$, ix2 + 1))
n$ = LTRIM$(STR$(f1 + f2 + f3))
FOR j = 1 TO 2
IF MID$(n$, j, 1) <> MID$(n$, LEN(n$) + 1 - j, 1) THEN good = 0: EXIT FOR
NEXT
IF good THEN
factor f1 + f2 + f3, f$
IF VAL(f$) = f1 + f2 + f3 THEN
PRINT i, f1; f2; f3
END IF
END IF
END IF
END IF
END IF
END IF
NEXT
SUB factor (num, s$)
s$ = "": n = ABS(num): IF n > 0 THEN limit = sqroot(n): ELSE limit = 0
IF limit <> INT(limit) THEN limit = INT(limit + 1)
dv = 2: GOSUB DivideIt
dv = 3: GOSUB DivideIt
dv = 5: GOSUB DivideIt
dv = 7
DO UNTIL dv > limit
GOSUB DivideIt: dv = dv + 4 '11
GOSUB DivideIt: dv = dv + 2 '13
GOSUB DivideIt: dv = dv + 4 '17
GOSUB DivideIt: dv = dv + 2 '19
GOSUB DivideIt: dv = dv + 4 '23
GOSUB DivideIt: dv = dv + 6 '29
GOSUB DivideIt: dv = dv + 2 '31
GOSUB DivideIt: dv = dv + 6 '37
IF INKEY$ = CHR$(27) THEN s$ = CHR$(27): EXIT SUB
LOOP
IF n > 1 THEN s$ = s$ + STR$(n)
EXIT SUB
DivideIt:
DO
q = INT(n / dv)
IF q * dv = n AND n > 0 THEN
n = q: s$ = s$ + STR$(dv): IF n > 0 THEN limit = sqroot(n): ELSE limit = 0
IF limit <> INT(limit) THEN limit = INT(limit + 1)
ELSE
EXIT DO
END IF
LOOP
RETURN
END SUB
finds 32123, with prime factors 7, 13, 353, which add to 373, a prime. The sum of digits of 32123 is 11.
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Posted by Charlie
on 2007-04-19 12:05:26 |