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A103506
Smallest prime p such that 2n+1 = 2q + p for some odd prime q, or 0 if no such prime exists.
9
0, 0, 0, 3, 5, 3, 5, 3, 5, 7, 13, 3, 5, 3, 5, 7, 13, 3, 5, 3, 5, 7, 13, 3, 5, 7, 17, 11, 13, 3, 5, 3, 5, 7, 13, 11, 13, 3, 5, 7, 37, 3, 5, 3, 5, 7, 13, 3, 5, 7, 17, 11, 13, 3, 5, 7, 29, 11, 13, 3, 5, 3, 5, 7, 13, 11, 13, 3, 5, 7, 37, 3, 5, 3, 5, 7, 13, 11
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=11, 2*11+1 = 23 = 2*5+13, thus a(11)=13.
MATHEMATICA
Join[{0, 0, 0}, Table[m=3; While[! (PrimeQ[m] && (((n-m)/2) > 2) && PrimeQ[(n-m)/2]), m=m+2]; m, {n, 9, 299, 2}]]
PROG
(Scheme) (define (A103506 n) (let ((ind (A103509 n))) (if (zero? ind) 0 (A000040 ind)))) -- Antti Karttunen, Jun 19 2007
CROSSREFS
a(n)=0 if A103509(n)=0, otherwise A000040(A103509(n)).
Sequence in context: A010703 A107489 A152050 * A094929 A096634 A105439
KEYWORD
nonn
AUTHOR
Lei Zhou, Feb 09 2005
EXTENSIONS
Edited by Antti Karttunen, Jun 19 2007
STATUS
approved