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Three-dimensional plotof 100,000 values generated with RANDU. Each point represents 3 consecutive pseudorandom values. It is clearly seen that the points fall in 15two-dimensionalplanes.RANDUis alinear congruentialpseudorandom number generatorof theParkMiller type, which has been used since the 1960s.[1]It is defined by therecurrence:

with the initial seed number,as anodd number. It generates pseudorandomintegerswhich areuniformly distributedin the interval[1, 231 1], but in practical applications are often mapped into pseudorandomrationalsin the interval(0, 1), by the formula:.It is widely considered to be one of the most ill-conceived random number generators ever designed.[citation needed]It fails thespectral testbadly for dimensions greater than 2, and every integer result is odd. However, at least eight low-order bits are dropped when converted to single-precision floating-point.The reason for choosing these particular values is that with a 32-bit-integer word size, the arithmetic of mod 231andcalculations could be done quickly, using special features of some computer hardware.We'll get right to it: Today we ask you to help Wikipedia. We survive on donations averaging about50 lei. If we all gave10 lei, the fundraiser would be over in an hour.DONATE NOWProblems with multiplier and modulus[edit]To show the problem with these values, of multiplier 65539 and modulus 231, consider the following calculation where every term should be taken mod 231. Start by writing the recursive relation as:

which becomes, after expanding the quadratic factor:

because232mod 231= 0and allows us to show the correlation between three points as:

As a result of this correlation, the points in three-dimensional space (mod 231) fall in 15 planes.[2]As a result of the wide use of RANDU in the early 1970s, many results from that time are seen as suspicious.[3]