A138965 Least prime factor of concatenation of first n odd numbers.

1, 13, 3, 23, 37, 3, 11617, 5, 3, 135791113151719, 29, 3, 5, 11, 3, 135791113151719212325272931, 17, 3, 7, 13, 3, 131, 5, 3, 11, 25471443030907588399109, 3, 5, 7, 3, 181, 41, 3, 135791113151719212325272931333537394143454749515355575961636567, 19, 3, 40351, 5, 3, 7, 11, 3, 5, 57041, 3, 351269, 11, 3, 135791113151719212325272931333537394143454749515355575961636567697173757779818385878991939597

Offset

1,2

Links

Sean A. Irvine, Table of n, a(n) for n = 1..300

F. Smarandache, Sequences of numbers involved in unsolved problems, arXiv:math/0604019

Formula

A138965(n) = A020639(A019519(n)) (= 3 if n = 0 (mod 3)).

Prog

(PARI) t=1; for( n=2, 99, print1( factor( eval( t=Str( t, 2*n-1 )))[1, 1], ", "))

Crossrefs

Cf. A019519, A046036, A048847; A109837, A104644.

Sequence in context: A213538 A264971 A107806 * A317313 A170922 A005602

Adjacent sequences: A138962 A138963 A138964 * A138966 A138967 A138968

Keyword

base,nonn

Author

M. F. Hasler, Apr 14 2008

Status

approved