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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 Antti Karttunen, Table of n, a(n) for n = 1..15120 Antti Karttunen, Data supplement: n, a(n) computed for n = 1..100000 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 Cf. A010051, A059841. Bisection of A322977. Sequence in context: A279507 A054656 A080096 * A294142 A068915 A302193 Adjacent sequences: A322975 A322976 A322977 * A322979 A322980 A322981 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.)