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A306544 Any positive integer n has a smallest multiple consisting of a succession of 1's followed by a succession of 0's (A052983). This multiple is regarded as a binary number and a(n) is its conversion to base 10. 0
2, 2, 14, 4, 2, 14, 126, 8, 1022, 2, 6, 28, 126, 126, 14, 16, 131070, 1022, 524286, 4, 126, 6, 8388606, 56, 4, 126, 268435454, 252, 536870910, 14, 65534, 32, 126, 131070, 126, 2044, 14, 524286, 126, 8, 62, 126, 4194302, 12, 1022, 8388606, 140737488355326, 112, 8796093022206 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For any odd number m not divisible by 5 (A045572), Euler's theorem (lcm(9*m,10) = 1, so 10^phi(9*m) == 1 (mod 9*m); i.e., 9*m | 10^d - 1 = 9*R_d with d = phi(9*m)) guarantees that the repunit R_d is always some multiple of m.

The numbers of the form 2^i*5^j with i, j >= 0 (A003592) clearly have a multiple equal to 10^r, for r = max(i,j).

These multiples of n end in a string of one or more 0's, so all the terms of this sequence are even.

The powers 2^k are fixed points of this sequence: the smallest multiple of 2^k consisting of a succession of 1's followed by a succession of 0's is 10^k, and 10^k in base 2 is 2^k in base 10.

LINKS

Table of n, a(n) for n=1..49.

Makoto Kamada, Factorization of 11...11 (Repunit).

EXAMPLE

The smallest multiple of the integer 7 consisting of a succession of 1's followed by a succession of 0's is 1111110, and 1111110_2 = 126_10, so a(7) = 126. This is also the case for n=13, 14, 21, 26, 33, 35, 37, ...

CROSSREFS

Cf. A000079, A052983, A045572, A099679, A002275, A007088, A276349, A003592, A011557, A276348.

Sequence in context: A282460 A327930 A068511 * A060590 A129083 A045685

Adjacent sequences:  A306541 A306542 A306543 * A306545 A306546 A306547

KEYWORD

nonn,base

AUTHOR

Bernard Schott, Feb 22 2019

EXTENSIONS

More terms from Michel Marcus, Feb 28 2019

STATUS

approved

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Last modified June 2 07:15 EDT 2020. Contains 334767 sequences. (Running on oeis4.)