OFFSET
1,1
COMMENTS
Motivated by the observation from A. Wesolowski that Sophie Germain primes A005384 satisfy this relation. A005384 is indeed exactly the subsequence of all primes in this sequence.
If p is an odd prime and 8*p+1 is in A006881, then 4*p is in the sequence. - Robert Israel, May 11 2016
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
filter:= n -> numtheory:-tau(4*n+2)=numtheory:-tau(4*n)-2:
select(filter, [$1..1000]); # Robert Israel, May 11 2016
MATHEMATICA
Select[Range@ 800, DivisorSigma[0, 4 # + 2] == DivisorSigma[0, 4 #] - 2 &] (* Michael De Vlieger, May 12 2016 *)
PROG
(PARI) for(n=1, 999, numdiv(4*n+2)==numdiv(4*n)-2 & print1(n", "))
(Magma) [n: n in [1..764] | NumberOfDivisors(4*n+2) eq NumberOfDivisors(4*n)-2]; // Arkadiusz Wesolowski, May 11 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, Aug 25 2012
STATUS
approved