#include "isprime.bas"

function nextprime( n as uinteger ) as uinteger
    'finds the next prime after n
    if n = 0 then return 2
    if n < 3 then return n + 1
    dim as integer q = n + 2
    while not isprime(q)
        q+=2
    wend
    return q
end function

function spd( byval n as integer, d() as integer ) as boolean
    if not isprime(n) then return false
    for i as integer = lbound(d) to ubound(d)
        if not nextprime(n) = n + d(i) then return false
        n+=d(i)
    next i
    return true
end function

sub print_set( byval n as uinteger, d() as uinteger )
    print "( ";n;" ";
    for i as integer = lbound(d) to ubound(d)
        print n+d(i);" ";
        n+=d(i)
    next i
    print ")"
end sub

function count_below( max as uinteger, d() as uinteger ) as uinteger
    dim as uinteger c = 0, last = 0
    for n as uinteger = 2 to max-d(ubound(d))
        if spd(n, d()) then
            c+=1
            if c=1 then print_set( n, d() )
            last = n
        end if
    next n
    print_set(last, d())
    return c
end function

dim as integer n, c

'example 1, differences of 2
redim as uinteger d(0)
d(0) = 2
print "Differences of 2 (the twin primes)"
c = count_below(1000000, d())
print "Number of occurrences: ", c

'example 2, difference of 1
d(0) = 1
print
print "Differences of 1"
c = count_below(1000000, d())
print "Number of occurrences: ", c

'example 3, differences of 2,2
redim as uinteger d(1)
d(0) = 2 : d(1) = 2
print
print "Differences of 2, 2"
c = count_below(1000000, d())
print "Number of occurrences: ", c

'example 4, differences of 2,4
d(1) = 4
print
print "Differences of 2, 4"
c = count_below(1000000, d())
print "Number of occurrences: ", c

'example 5, differences of 2,2
d(0) = 4 : d(1) = 2
print
print "Differences of 4, 2"
c = count_below(1000000, d())
print "Number of occurrences: ", c

'example 6, differences of 6,4,2
redim as uinteger d(2)
d(0) = 6 : d(1) = 4 : d(2) = 2
print
print "Differences of 6, 4, 2"
c = count_below(1000000, d())
print "Number of occurrences: ", c