|
|
A238778
|
|
Sum of all primes p such that 2n - p is also a prime.
|
|
4
|
|
|
2, 3, 8, 15, 12, 21, 32, 36, 40, 55, 72, 65, 56, 90, 64, 119, 144, 57, 120, 168, 132, 161, 240, 200, 156, 270, 168, 203, 360, 155, 320, 396, 136, 350, 432, 333, 380, 546, 320, 369, 672, 387, 352, 810, 368, 423, 672, 294, 600, 816, 520, 583, 864, 660, 784
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
2,1
|
|
COMMENTS
|
Sum of n-th row in triangle A171637.
|
|
LINKS
|
|
|
FORMULA
|
|
|
PROG
|
(Haskell)
a238778 n = sum $ filter ((== 1) . a010051') $
map (2 * n -) $ takeWhile (<= 2 * n) a000040_list
(PARI) a(n) = my(s=0); forprime(p=2, 2*n, if(isprime(2*n-p), s+=p)); s; \\ Michel Marcus, Jan 24 2022
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|