

A103153


a(n) is the smallest odd prime p such that 2*n+1 = 2*p + A000040(k) for some k>1, or 0 if no such prime exists.


8



0, 0, 0, 3, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 7, 5, 3, 3, 5, 5, 3, 7, 3, 3, 5, 3, 7, 5, 3, 7, 5, 3, 3, 5, 5, 3, 7, 3, 3, 5, 5, 3, 7, 3, 19, 5, 3, 7, 5, 11, 3, 11, 3, 3, 5, 3, 3, 5, 3, 7, 5, 11, 7, 11, 11, 3, 11, 3, 13, 5, 3, 3, 5, 5, 7, 7, 3, 3, 5, 5, 3, 7, 5, 3, 7, 3, 13, 5, 3, 7, 5, 3, 3, 5, 5, 7, 7, 3
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OFFSET

1,4


LINKS



EXAMPLE

For n < 4 there are no such primes, thus a(1)a(3)=0. For n=4, 2*4+1 = 9 = 2*3+3, thus a(4)=3. For n=7, 2*7+1 = 15 = 2*5+5, thus a(7)=7.


MATHEMATICA

Do[m = 3; While[ ! (PrimeQ[m] && ((n  2*m) > 2) && PrimeQ[n  2*m]), m = m + 2]; Print[m], {n, 9, 299, 2}]


PROG



CROSSREFS

Cf. A195352 (similar definition, but p=2 is allowed).


KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



