订正:在小于1000的四素数应去掉(11,13,17,19)一组,还有2组。
另:小于3000的10内四素数有:
用错位法:
9,10,11,12,13,...........3000,
7,8,9,10,11,...............2998,
3,4,5,6,7,8...................2994,
1,2,3,4,5,...................2992
用公式2992(1-1/2)(1-2/3)(1-4/5)(1-4/7)(1-4/11)(1-4/13)(1-4/17)(1-4/19)(1-4/23)(1-4/29)(1-4/31).........(1-4/53)
=2992(1/2)(1/3)(1/5)(3/7)(7/11)(9/13)(13/17)(15/19)(19/23)(27/31)......(49/53)
=?
实际有(11,13,17,19),(191,193,197.199),(821,823,827,829),(1481,1483,1487,1489),(1871,1873,1877,1879),(2081,2083,2087,2089)六组,但(11,13,17,19)一组应是筛掉了。剩五组。 |