3. Quasi-amicable numbers

Search program for quasi-amicable numbers

The definition of amicable numbers is

σ(m)-m=n
σ(n)-n=m

and the definition of quasi-amicable numbers is

σ(m)-m-1=n
σ(n)-n-1=m

or

σ(m)=σ(n)=m+n+1.

So the program can be used in trivial change,

30   N=fnSigma(M)-M:if N<=M then 50
40   R=fnSigma(N)-N:if R=M then print M,N

into

30   N=fnSigma(M)-M-1:if N<=M then 50
40   R=fnSigma(N)-N-1:if R=M then print M,N

  There are 404 quasi-amicable pairs which smaller number is less than 10¹⁰.