A105428 Smallest prime dividing the composite near-repdigit number 133...33 consisting of a 1 followed by n 3's, where n=A105427.

7, 31, 67, 151, 23, 13, 7, 157, 163, 107, 17, 13, 7, 89, 170809, 31, 13, 7, 4363363, 251, 42169, 43, 13, 7, 641, 17, 6791, 109, 13, 7, 31, 29, 373, 261382937, 13, 7, 101921, 82647847, 443, 13, 7, 43, 1042402171, 71, 31, 13, 7, 1601, 425519761

Offset: 1

Author

Lekraj Beedassy, Apr 08 2005

Keywords

• nonn

Links

• FactorDB, Factorizations of (10^n-1)/3+10^n
• Makoto Kamada, Factorizations of 133...33.

Crossrefs

Cf. A089018.

Programs

Mathematica

Transpose[FactorInteger[#]][[1,1]]&/@DeleteCases[Table[ FromDigits[ PadRight[{1},n,3]],{n,2,60}],?PrimeQ] (* _Harvey P. Dale, Dec 10 2011 *)

PARI

for(n=1,100,m=10^n+(10^n-1)/3;if(!isprime(m),print1(factorint(m)[1,1]," "))) (Alekseyev)

Extensions

More terms from Max Alekseyev, Apr 11 2005