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%I #7 Sep 20 2012 16:58:26
%S 31,31331,313313331,31331333133331,31331333133331333331,
%T 313313331333313333313333331,31331333133331333331333333133333331,
%U 31331333133331333331333333133333331333333331
%N Threes and ones.
%C This sequence contains many primes.
%D F. Smarandache, Properties of numbers, University of Craiova, 1973
%F a(n) has increasing groups of 31, 331, ..., 33...31 (n times 3) concatenated.
%K nonn,easy,base,less
%O 1,1
%A Jan Jensen (dorul(AT)post6.tele.dk)
%E More terms from _Erich Friedman_.