OFFSET
1,1
COMMENTS
Besides the 1st, 2nd, and 4th terms, a(n) is 2 times a prime, one of a(n)-1 or a(n)+1 is a prime, and the other number is 3 times a prime.
The 10 in the definition is the smallest value for which this is a possibly infinite list.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
For a(3)=14, sigma_0(13)=2, sigma_0(14)=4, and sigma_0(15)=4, hence sigma_0(a(3)-1) + sigma_0(a(3)) + sigma_0(a(3)+1) = 10.
MAPLE
Res:= 7, 12, 14, 18: count:= 4:
p:= 9:
while count < 100 do
p:= nextprime(p);
n:= 2*p;
if n mod 3 = 1 then v:= isprime(n+1) and isprime((n-1)/3)
else v:= isprime(n-1) and isprime((n+1)/3)
fi;
if v then count:= count+1; Res:= Res, n fi
od:
Res; # Robert Israel, Aug 27 2018
MATHEMATICA
Select[Partition[Range[10^4], 3, 1], Total@ DivisorSigma[0, #] == 10 &][[All, 2]] (* Michael De Vlieger, Aug 05 2018 *)
PROG
(PARI) isok(n) = numdiv(n-1) + numdiv(n) + numdiv(n+1) == 10; \\ Michel Marcus, Aug 04 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Kevin D. Woerner, Aug 03 2018
STATUS
approved