OFFSET
2,1
EXAMPLE
n=2: 2nd repunit=11, 13-7=6=a[2].
MATHEMATICA
<<NumberTheory`NumberTheoryFunctions` Table[NextPrime[(10^n-1)/9]-PreviousPrime[(10^n-1)/9], {n, 2, 100}]
dpf[n_]:=Module[{ru=FromDigits[PadRight[{}, n, 1]]}, NextPrime[ru]-NextPrime[ ru, -1]]; Array[dpf, 60, 2] (* Harvey P. Dale, Sep 06 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jul 09 2004
STATUS
approved