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

1,1

Links

Table of n, a(n) for n=1..49.

FactorDB, Factorizations of (10^n-1)/3+10^n

Makoto Kamada, Factorizations of 133...33.

Mathematica

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

Prog

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

Crossrefs

Cf. A089018.

Sequence in context: A255414 A031388 A163354 * A050547 A157914 A090684

Adjacent sequences: A105425 A105426 A105427 * A105429 A105430 A105431

Keyword

nonn

Author

Lekraj Beedassy, Apr 08 2005

Extensions

More terms from Max Alekseyev, Apr 11 2005

Status

approved