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A283107
Numbers k such that tau(4*(k - 1)) is prime.
1
2, 5, 17, 257, 1025, 16385, 65537, 1048577, 67108865, 268435457, 17179869185, 274877906945, 1099511627777, 17592186044417, 1125899906842625, 72057594037927937, 288230376151711745
OFFSET
1,1
COMMENTS
Conjecturally, a supersequence of A281312.
The conjecture is true: the formula at A281312 implies that the number of divisors of 4*A281312(n) - 4 is A000043(n+1). - Charles R Greathouse IV, Mar 01 2017
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..467
MATHEMATICA
Select[Range[2, 10^7], PrimeQ@ DivisorSigma[0, 4 (# - 1)] &] (* Michael De Vlieger, Feb 28 2017 *)
PROG
(Magma) [n: n in [2..1100000] | IsPrime(NumberOfDivisors(4*(n-1)))];
(PARI) is(n)=isprime(numdiv(4*n-4)) \\ Charles R Greathouse IV, Feb 28 2017
(PARI) list(lim)=my(v=List()); forprime(p=3, logint(lim\1*8-8, 2), listput(v, 2^(p-3)+1)); Vec(v) \\ Charles R Greathouse IV, Mar 01 2017
CROSSREFS
Supersequence of A281312.
Sequence in context: A067339 A309178 A096848 * A269834 A290200 A132198
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(4), a(9)-a(17) from Charles R Greathouse IV, Mar 01 2017
STATUS
approved