OFFSET
1,4
COMMENTS
If a(n)=2, then prime(n)+2 and prime(n)-2 are both semiprimes; that is, prime(n) belongs to A063643. - Michel Marcus, Mar 26 2015
MATHEMATICA
sks[n_]:=Module[{k=1, p=Prime[n]}, While[PrimeOmega[p+k]!=2||PrimeOmega[p-k]!=2||p-k<4, If[p-k<3, Break[]]; k++]; If[p-k<4, 0, k]]; Array[sks, 80] (* Harvey P. Dale, Dec 09 2016 *)
PROG
(PARI) a(n) = {p = prime(n); for (k=1, p-1, if ((bigomega(p-k)==2) && (bigomega(p+k) == 2), return (k)); ); return (0); } \\ Michel Marcus, Apr 25 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Apr 25 2014
EXTENSIONS
More terms from Michel Marcus, Apr 25 2014
Name edited by Michel Marcus, Mar 26 2015
STATUS
approved