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PROG
| (PARI) twtotwp2(n, n2, k) = { local(x, y, x2, c); c=0; forprime(x=n, n2, x2=x+2; y=x^x2+k; if(y%x2==0&!isprime(x2), c++; print1(x+2", "); ); ); print(); print(c", "pitwin(n2)) } pitwins(n) = \The number of twin prime pairs <= n. { local(c, x); c=0; forprime(x=3, n, if(isprime(x+2), c++) ); return(c) }
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