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A284599
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Sum of twin prime (A001097) divisors of n.
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2
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0, 0, 3, 0, 5, 3, 7, 0, 3, 5, 11, 3, 13, 7, 8, 0, 17, 3, 19, 5, 10, 11, 0, 3, 5, 13, 3, 7, 29, 8, 31, 0, 14, 17, 12, 3, 0, 19, 16, 5, 41, 10, 43, 11, 8, 0, 0, 3, 7, 5, 20, 13, 0, 3, 16, 7, 22, 29, 59, 8, 61, 31, 10, 0, 18, 14, 0, 17, 3, 12, 71, 3, 73, 0, 8, 19, 18, 16, 0, 5, 3, 41, 0, 10, 22, 43, 32, 11, 0, 8
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OFFSET
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1,3
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LINKS
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FORMULA
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a(n) = Sum_{d|n, d twin prime} d.
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EXAMPLE
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a(15) = 8 because 15 has 4 divisors {1, 3, 5, 15} among which 2 are twin primes {3, 5} therefore 3 + 5 = 8.
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MAPLE
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N:= 200: # to get a(1)..a(N)
P:= select(isprime, {seq(i, i=3..N+2)}):
TP:= P intersect map(`-`, P, 2):
TP:= TP union map(`+`, TP, 2):
V:= Vector(N):
for p in TP do
pm:= [seq(i, i=p..N, p)];
V[pm]:= map(`+`, V[pm], p);
od:
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MATHEMATICA
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Table[Total[Select[Divisors[n], PrimeQ[#1] && (PrimeQ[#1 - 2] || PrimeQ[#1 + 2]) &]], {n, 80}]
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PROG
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(Python)
from sympy import divisors, isprime
def a(n): return sum([i for i in divisors(n) if isprime(i) and (isprime(i - 2) or isprime(i + 2))])
(PARI) a(n) = sumdiv(n, d, d*(isprime(d) && (isprime(d-2) || isprime(d+2)))); \\ Michel Marcus, Apr 02 2017
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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