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 A065985 Numbers n such that d(n) / 2 is prime, where d(n) = number of divisors of n. 1
 6, 8, 10, 12, 14, 15, 18, 20, 21, 22, 26, 27, 28, 32, 33, 34, 35, 38, 39, 44, 45, 46, 48, 50, 51, 52, 55, 57, 58, 62, 63, 65, 68, 69, 74, 75, 76, 77, 80, 82, 85, 86, 87, 91, 92, 93, 94, 95, 98, 99, 106, 111, 112, 115, 116, 117, 118, 119, 122, 123, 124, 125, 129, 133, 134 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Harry J. Smith, Table of n, a(n) for n = 1..1000 MATHEMATICA Select[Range[1, 1000], PrimeQ[DivisorSigma[0, # ] / 2] == True &] PROG (PARI) n=0; for (m=1, 10^9, f=numdiv(m)/2; if (frac(f)==0 && isprime(f), write("b065985.txt", n++, " ", m); if (n==1000, return))) \\ Harry J. Smith, Nov 05 2009 (PARI) is(n)=n=factorback(factor(n)[, 2])/2; denominator(n)==1 && isprime(n) \\ Charles R Greathouse IV, Oct 15 2015 CROSSREFS Sequence in context: A064176 A000379 A176525 * A233421 A060652 A020739 Adjacent sequences:  A065982 A065983 A065984 * A065986 A065987 A065988 KEYWORD nonn AUTHOR Joseph L. Pe, Dec 10 2001 STATUS approved

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Last modified July 24 02:56 EDT 2019. Contains 325290 sequences. (Running on oeis4.)