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A158911
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Numbers of the form 2^i*5^j - 1.
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1
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0, 1, 3, 4, 7, 9, 15, 19, 24, 31, 39, 49, 63, 79, 99, 124, 127, 159, 199, 249, 255, 319, 399, 499, 511, 624, 639, 799, 999, 1023, 1249, 1279, 1599, 1999, 2047, 2499, 2559, 3124, 3199, 3999, 4095, 4999, 5119, 6249, 6399, 7999, 8191, 9999, 10239
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Numbers n such that 10^n is divisible by n+1.
Numbers n such that the prime divisors of n+1 are also divisors of the numbers m obtained by the concatenation of n and n+1. For example, for n=39, m = 3940, the divisors of 40 are {2, 5} and the divisors of 3940 are {2, 5, 197}. [From Michel Lagneau (mn.lagneau2(AT)orange.fr , Dec 20 2011].
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LINKS
| Peter Pein, Table of n, a(n) for n = 1..134
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FORMULA
| a(n) = A003592(n) - 1.
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MATHEMATICA
| fQ[n_] := PowerMod[10, n, n + 1] == 0; Select[ Range[0, 11000], fQ] [From Robert G. Wilson v (rgwv(AT)rgwv.com), Sep 08 2010]
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PROG
| (PARI) is(n)=n=(n+1)>>valuation(n+1, 2); ispower(n, , &n); n==1||n==5 \\ Charles R Greathouse IV, Jan 12 2012
(PARI) list(lim)=my(v=List(), N); lim++; for(n=0, log(lim)\log(5), N=5^n; while(N<=lim, listput(v, N-1); N<<=1)); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jan 12 2012
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CROSSREFS
| Cf. A158520, A034887, A129344.
Sequence in context: A163468 A069183 A119907 * A086772 A169898 A086336
Adjacent sequences: A158908 A158909 A158910 * A158912 A158913 A158914
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KEYWORD
| easy,nonn
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AUTHOR
| Ctibor O. Zizka (c.zizka(AT)email.cz), Mar 30 2009
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EXTENSIONS
| Corrected by Claudio Meller, Rick Shepherd, Charles R Greathouse IV and R. J. Mathar, Aug 23 2010
Edited by N. J. A. Sloane, Aug 25 2010, Oct 04 2010
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