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A322978 Number of even divisors d of 2n such that d-1 is prime. 4
0, 1, 1, 2, 0, 3, 1, 2, 2, 2, 0, 5, 0, 2, 2, 3, 0, 4, 1, 3, 3, 2, 0, 6, 0, 1, 3, 3, 0, 6, 1, 3, 1, 2, 1, 7, 1, 2, 1, 4, 0, 6, 0, 3, 4, 1, 0, 7, 2, 2, 2, 3, 0, 6, 1, 3, 3, 1, 0, 8, 0, 2, 4, 4, 0, 5, 0, 3, 2, 4, 0, 8, 0, 2, 3, 4, 1, 3, 1, 5, 3, 2, 0, 9, 0, 1, 2, 3, 0, 9, 2, 2, 2, 1, 1, 8, 1, 3, 3, 4, 0, 5, 0, 3, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
LINKS
FORMULA
a(n) = A322977(2*n).
a(n) = Sum_{d|(2*n), d>1} A059841(d)*A010051(d-1).
MATHEMATICA
Array[DivisorSum[2 #, 1 &, And[EvenQ@ #, PrimeQ[# - 1]] &] &, 105] (* Michael De Vlieger, Jan 04 2019 *)
PROG
(PARI) A322978(n) = sumdiv(n+n, d, (!(d%2))*isprime(d-1));
(PARI)
A322977(n) = sumdiv(n, d, (!(d%2))*isprime(d-1));
A322978(n) = A322977(n+n);
CROSSREFS
Bisection of A322977.
Sequence in context: A279507 A054656 A080096 * A294142 A068915 A302193
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jan 04 2019
STATUS
approved

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Last modified May 22 13:22 EDT 2024. Contains 372755 sequences. (Running on oeis4.)