OFFSET
1,1
COMMENTS
Conjecture: this sequence is infinite.
Or, primes p such that d(2p+1)=8. - Zak Seidov, Sep 07 2016
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
Consider 67. Then 67*(2*67+1) = 9045 and d(9045) = 16.
MATHEMATICA
Select[Prime@ Range@ 256, DivisorSigma[0, # (2 # + 1)] == 16 &] (* Michael De Vlieger, Aug 30 2016 *)
PROG
(PARI) lista(nn) = forprime (p=2, nn, if (numdiv(p*(2*p+1)) == 16, print1(p, ", "))); \\ Michel Marcus, Aug 29 2016
(PARI) is(n)=numdiv(2*n+1)==8 && isprime(n) \\ Charles R Greathouse IV, Aug 29 2016
(Magma) [n: n in [0..2000] | NumberOfDivisors(2*n+1) eq 8 and IsPrime(n)]; // Vincenzo Librandi, Aug 30 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Anthony Hernandez, Aug 29 2016
EXTENSIONS
Corrected and extended by Michel Marcus, Aug 29 2016
STATUS
approved