OFFSET
0,1
EXAMPLE
a(1)=5 because 5 + 5 (mod 3) = 7,
a(2)=11 because 11 + 11 (mod 3) = 11 + 11 (mod 9) = 13.
a(3)=17 because 17 + 17 (mod 3) = 17 + 17 (mod 5) = 17 + 17 (mod 15) = 19,
a(4)=67 because 67 + 67 (mod 7) = 67 + 67 (mod 9) = 67 + 67 (mod 21) = 67 + 67 (mod 63) = 71,
a(5)=101 because 101 + 101 (mod 3) = 101 + 101 (mod 9) = 101 + 101 (mod 11) = 101 + 101 (mod 33) = 101 + 101 (mod 99), etc.
MATHEMATICA
f[n_] := Block[{p = Prime@n, np = Prime[n + 1]}, Length@ Select[ Divisors[2p - np], # >= np - p &]]; t = Table[0, {50}]; Do[ a = f@n; If[a < 50 && t[[a + 1]] == 0, t[[a + 1]] = n; Print[{a, n, Prime@n}]], {n, 100000}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Rémi Eismann and Robert G. Wilson v, May 14 2006
EXTENSIONS
Edited by M. F. Hasler, Nov 07 2009
STATUS
approved