1,1

13781 is OK since 13782, 13783, 13784, 13785 and 13786 all have 8 divisors:

{1,2,3,6,2297,4594,6891,13782}, {1,7,11,77,179,1253,1969,13783},

{1,2,4,8,1723,3446,6892,13784}, {1,3,5,15,919,2757,4595,13785} and

{1,2,61,113,122,226,6893,13786}.

Select[Prime@Range[1000000], DivisorSigma[0, #+1]==DivisorSigma[0, #+2]==DivisorSigma[0, #+3]==DivisorSigma[0, #+4]==DivisorSigma[0, #+5]&]

Cf. A008329, A049234.

Sequence in context: A047827 A157669 A031807 this_sequence A109102 A013821 A013912

Adjacent sequences: A119727 A119728 A119729 this_sequence A119731 A119732 A119733

nonn

Zak Seidov (zakseidov(AT)yahoo.com), Jul 29 2006