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A105047 Form an addition table of the primes; a(n) is the number of even numbers that appear for the first time in column n. 3
1, 1, 2, 2, 3, 3, 3, 3, 3, 3, 5, 4, 5, 3, 4, 3, 3, 7, 4, 5, 4, 3, 5, 5, 6, 5, 5, 4, 4, 3, 7, 5, 5, 7, 5, 5, 6, 4, 6, 5, 5, 7, 4, 6, 5, 4, 6, 5, 8, 5, 7, 4, 5, 6, 5, 3, 3, 8, 8, 5, 4, 5, 8, 8, 5, 5, 9, 4, 8, 7, 7, 6, 6, 5, 5, 7, 5, 7, 7, 6, 6, 6, 6, 5, 7, 7, 6, 6, 5, 6, 5, 5, 7, 4, 8, 4, 8, 5, 8, 7, 8, 9, 7, 5, 9 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
For n > 2: a(n) = A102696(n-1) - A102696(n-2); a(n+1) = length of n-th row in the triangle A260580. - Reinhard Zumkeller, Aug 11 2015
LINKS
Eric Weisstein's World of Mathematics, Goldbach Partition
EXAMPLE
The addition table is as follows:
+ | 2 3 5 7 11
--+--------------
2 | 4 5 7 9 13
3 | 6 8 10 14
5 | 10 12 16
7 | 14 18
11 | 22
PROG
(PARI) lista(n) = {maxp = prime(n); v = vector(maxp); forprime (p=1, maxp, nb = 0; forprime (q=1, p, s = p+q; if (! (s % 2), if (!v[s/2], nb++); v[s/2] = 1; ); ); print1(nb, ", "); ); } \\ Michel Marcus, Apr 18 2013
(Haskell)
a105047 1 = 1
a105047 n = length $ a260580_row (n - 1)
-- Reinhard Zumkeller, Aug 11 2015
CROSSREFS
Sequence in context: A156081 A368991 A147954 * A331135 A089881 A251547
KEYWORD
nonn
AUTHOR
Andrew S. Plewe, Apr 06 2005
EXTENSIONS
More terms from Reinhard Zumkeller, Apr 19 2005
STATUS
approved

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Last modified June 24 15:31 EDT 2024. Contains 373679 sequences. (Running on oeis4.)