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A305939 Number of powers of 9 having exactly n digits '0' (in base 10), conjectured.

%I A305939 #6 Jun 23 2018 09:18:50
%S A305939 12,7,18,3,9,13,11,11,6,9,17,15,12,9,11,6,9,9,9,13,16,9,10,7,7,9,9,13,
%T A305939 14,15,14,15,9,9,8,8,15,11,11,12,5,12,14,5,7,14,10,8,5,16,12
%N A305939 Number of powers of 9 having exactly n digits '0' (in base 10), conjectured.
%C A305939 a(0) = 12 is the number of terms in A030705 and in A195945, which includes the power 7^0 = 1.
%C A305939 These are the row lengths of A305929. It remains an open problem to provide a proof that these rows are complete (as for all terms of A020665), but the search has been pushed to many orders of magnitude beyond the largest known term, and the probability of finding an additional term is vanishing, cf. Khovanova link.
%H A305939 M. F. Hasler, <a href="/wiki/Zeroless_Powers">Zeroless powers</a>, OEIS Wiki, March 2014, updated 2018.
%H A305939 T. Khovanova, <a href="https://blog.tanyakhovanova.com/2011/02/86-conjecture/">The 86-conjecture</a>, Tanya Khovanova's Math Blog, Feb. 2011.
%H A305939 W. Schneider, <a href="http://web.archive.org/web/20050407120908/http://www.wschnei.de:80/digit-related-numbers/nozeros.html">No Zeros</a>, 2000, updated 2003. (On web.archive.org--see A007496 for a cached copy.)
%o A305939 (PARI) A305939(n,M=99*n+199,x=9)=sum(k=0,M,#select(d->!d,digits(x^k))==n)
%o A305939 (PARI) A305939_vec(nMax,M=99*nMax+199,x=9,a=vector(nMax+=2))={for(k=0,M,a[min(1+#select(d->!d,digits(x^k)),nMax)]++);a[^-1]}
%Y A305939 Cf. A030705 = row 0 of A305929: k such that 9^k has no 0's; A195945: these powers 9^k.
%Y A305939 Cf. A020665: largest k such that n^k has no '0's.
%Y A305939 Cf. A063626 = column 1 of A305929: least k such that 9^k has n digits 0 in base 10.
%Y A305939 Cf. A305942 (analog for 2^k), ..., A305947, A305938 (analog for 8^k).
%K A305939 nonn,base
%O A305939 0,1
%A A305939 _M. F. Hasler_, Jun 22 2018