create serial from number + reverse function

I need serials to be printed on documents and the serial has to be generated from a base number. for example newserial = createSerial( numX ); newserial : is a new serial number 7 digits long; numX is used to create the newserial number; There needs to be a way that given newserial and numX that i can determine that newserial is a valid serial for numX ( no other value but numX will return true) bool = verifserial( newserial, numX ) serials also needed be be able to be returned due to there order of creation. e.g. serialnum = getGeneratedSerial( numX, Order ) Order is a number e.g. 1 that would return the first serial number generatoed by newserial = createSerial( numX ); e.g. /////////////////////////////////////////////////// newserial1 = createSerial( numX ); newserial2 = createSerial( numX ); newserial3 = createSerial( numX ); serialnum1 = getGeneratedSerial( numX, 1) serialnum2 = getGeneratedSerial( numX, 2) serialnum3 = getGeneratedSerial( numX, 3) newserial1 ,newserial2, newserial3 are new serials numbers generated from numX. such that verifserial( newserial, numX ) returns true only for numX. serialnum1 would return newserial1 serialnum2 would return newserial2 serialnum3 would return newserial3 /////////////////////////////////////// please in your bid requests explain the math behind the solution i need the functions newserial = createSerial( numX ); bool = verifserial( newSerial, numX ) serialnum = getGeneratedSerial( numX, Order) ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform C#