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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
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
(Scheme:) (define (A103153 n) (let ((ind (A103507 n))) (if (zero? ind) 0 (A000040 ind))))
CROSSREFS
a(n)=0 if A103507(n)=0, otherwise A000040(A103507(n)).
Cf. A195352 (similar definition, but p=2 is allowed).
Sequence in context: A049613 A002373 A236569 * A162022 A318240 A262289
KEYWORD
nonn
AUTHOR
Lei Zhou, Feb 09 2005
EXTENSIONS
Edited and Scheme code added by Antti Karttunen, Jun 19 2007
Definition corrected by Hugo Pfoertner, Sep 16 2011
STATUS
approved