OFFSET
4,1
LINKS
Zhi-Wei Sun, Table of n, a(n) for n = 4..10000
Zhi-Wei Sun, An amazing conjecture on primes, a message to Number Theory List, Nov. 27, 2012.
Zhi-Wei Sun, Conjectures involving primes and quadratic forms, arXiv:1211.1588.
EXAMPLE
a(6)=7 since 6=2+4 with 2*4-1=7 prime.
MATHEMATICA
Do[Do[If[PrimeQ[k(n-k)-1]==True, Print[n, " ", k(n-k)-1]; Goto[aa]], {k, 1, n/2}]; Print[n, " ", counterexample]; Label[aa]; Continue, {n, 4, 100}]
Table[k = 1; While[p = k*(n - k) - 1; k <= n/2 && ! PrimeQ[p], k++]; If[k > n/2, Print["counterexample at n=", n]; p = 0]; p, {n, 4, 100}] (* T. D. Noe, Nov 28 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Zhi-Wei Sun, Nov 28 2012
STATUS
approved