login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A305942
Number of powers of 2 having exactly n digits '0' (in base 10), conjectured.
10
36, 41, 31, 34, 25, 32, 37, 23, 43, 47, 33, 35, 29, 27, 27, 39, 34, 34, 28, 29, 31, 30, 38, 25, 35, 35, 36, 40, 32, 40, 43, 39, 32, 30, 30, 32, 36, 39, 23, 26, 31, 37, 27, 28, 33, 39, 28, 44, 34, 27, 43, 33, 27, 32, 31, 27, 27, 32, 35, 34, 36, 28, 32, 39, 38, 40, 28, 43, 38, 32, 22
OFFSET
0,1
COMMENTS
a(0) = 36 is the number of terms in A007377 and in A238938, which includes the power 2^0 = 1.
These are the row lengths of A305932. 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.
The average of the first 100000 terms is ~33.219 with a minimum of 12 and a maximum of 61. - Hans Havermann, Apr 26 2020
LINKS
M. F. Hasler, Zeroless powers, OEIS Wiki, March 2014, updated 2018.
T. Khovanova, The 86-conjecture, Tanya Khovanova's Math Blog, Feb. 2011.
W. Schneider, No Zeros, 2000, updated 2003. (On web.archive.org--see A007496 for a cached copy.)
PROG
(PARI) A305942(n, M=99*n+199)=sum(k=0, M, #select(d->!d, digits(2^k))==n)
(PARI) A305942_vec(nMax, M=99*nMax+199, a=vector(nMax+=2))={for(k=0, M, a[min(1+#select(d->!d, digits(2^k)), nMax)]++); a[^-1]}
CROSSREFS
Row lengths of A305932 (row n = exponents of 2^k with n '0's).
Cf. A007377 = {k | 2^k has no digit 0}; A238938: powers of 2 with no digit 0.
Cf. A298607: powers of 2 with the digit '0' in their decimal expansion.
Cf. A020665: largest k such that n^k has no digit 0 in base 10.
Cf. A031146: least k such that 2^k has n digits 0 in base 10.
Cf. A071531: least r such that n^r has a digit 0, in base 10.
Cf. A306112: largest k such that 2^k has n digits 0, in base 10.
Sequence in context: A181484 A060292 A334911 * A261265 A344808 A295694
KEYWORD
nonn,base
AUTHOR
M. F. Hasler, Jun 21 2018
STATUS
approved