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A070757 Number of ways to write 4n as a sum of 4 primes. 1
0, 1, 2, 3, 6, 7, 11, 13, 15, 21, 24, 26, 34, 38, 41, 50, 56, 57, 70, 77, 81, 96, 100, 109, 126, 129, 138, 156, 163, 175, 199, 198, 211, 239, 241, 258, 283, 281, 308, 335, 335, 360, 382, 385, 421, 445, 437, 482, 508, 503, 556, 571, 561, 632, 657, 645, 705, 726 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
LINKS
FORMULA
a(n) = A259194(4*n). - Robert Israel, Oct 29 2019
EXAMPLE
4*3 = 12 = 2+2+3+5 = 3+3+3+3 hence a(3)=2.
MAPLE
N:= 400: # to get a(0) to a(N/4)
Primes:= select(isprime, [$1..N]):
np:= nops(Primes):
for j from 0 to np do g[0, j]:= 1 od:
for n from 1 to 4 do
g[n, 0]:= 0:
for j from 1 to np do
g[n, j]:= convert(series(add(g[k, j-1]
*x^((n-k)*Primes[j]), k=0..n), x, N+1), polynom)
od
od:
seq(coeff(g[4, np], x, 4*i), i=1..N/4); # Robert Israel, Oct 29 2019
PROG
(PARI) a(n)={my(s=0); forprime(i=2, n, forprime(j=i, (4*n-i)\3, forprime(k=j, (4*n-i-j)\2, if(isprime(4*n-i-j-k), s++)))); s} \\ Andrew Howroyd, Oct 29 2019
CROSSREFS
Cf. A259194.
Sequence in context: A366641 A113545 A056825 * A056956 A171033 A269983
KEYWORD
nonn,look
AUTHOR
Benoit Cloitre, May 14 2002
EXTENSIONS
Corrected by Robert Israel, Oct 29 2019
STATUS
approved

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Last modified April 20 16:19 EDT 2024. Contains 371844 sequences. (Running on oeis4.)