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A103506
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Smallest prime p such that 2n+1 = 2q + p for some odd prime q, or 0 if no such prime exists.
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5
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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LINKS
| Hugo Pfoertner, Table of n, a(n) for n = 1..10000
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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.
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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}]]
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PROG
| (Scheme:) (define (A103506 n) (let ((ind (A103509 n))) (if (zero? ind) 0 (A000040 ind))))
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CROSSREFS
| a(n)=0 if A103509(n)=0, otherwise A000040(A103509(n)). Cf. A103151, A103152, A103153.
Sequence in context: A010703 A107489 A152050 * A094929 A096634 A105439
Adjacent sequences: A103503 A103504 A103505 * A103507 A103508 A103509
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KEYWORD
| nonn
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AUTHOR
| Lei Zhou (lzhou5(AT)emory.edu), Feb 09 2005
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EXTENSIONS
| Edited and Scheme-code added by Antti Karttunen (His-Firstname.His-Surname(AT)gmail.com), Jun 19 2007
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