p is a 4-digit prime number. p+30 is also prime. There are 9 primes from p to p+30 inclusive. What is p? What are the 9 primes in the nonuplet?
The 9 primes are:
1277 1279 1283 1289 1291 1297 1301 1303 1307
DefDbl A-Z
Dim crlf$, pr(9)
Function mform$(x, t$)
a$ = Format$(x, t$)
If Len(a$) < Len(t$) Then a$ = Space$(Len(t$) - Len(a$)) & a$
mform$ = a$
End Function
Private Sub Form_Load()
Text1.Text = ""
crlf$ = Chr(13) + Chr(10)
Form1.Visible = True
p = 1000
Do
p = nxtprm(p)
pr(0) = p
For i = 9 To 1 Step -1
pr(i) = pr(i - 1)
Next
If pr(9) > 0 Then
If pr(1) - pr(9) <= 30 Then
For i = 9 To 1 Step -1
Text1.Text = Text1.Text & pr(i) & " "
Next
Text1.Text = Text1.Text & crlf
End If
End If
DoEvents
Loop Until p > 10030
End Sub
Function prmdiv(num)
Dim n, dv, q
If num = 1 Then prmdiv = 1: Exit Function
n = Abs(num): If n > 0 Then limit = Sqr(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
Loop
If n > 1 Then prmdiv = n
Exit Function
DivideIt:
Do
q = Int(n / dv)
If q * dv = n And n > 0 Then
prmdiv = dv: Exit Function
Else
Exit Do
End If
Loop
Return
End Function
Function nxtprm(x)
Dim n
n = x + 1
While prmdiv(n) < n Or n < 2
n = n + 1
Wend
nxtprm = n
End Function
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Posted by Charlie
on 2017-12-27 12:47:03 |
computer solution (spoiler)
