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A155891 Least positive integer such that a(n)! starts with n, both written in binary. 6
1, 2, 3, 7, 6, 3, 5, 20, 7, 14, 6, 4, 10, 12, 5, 20, 27, 50, 7, 14, 23, 6, 13, 4, 25, 30, 10, 12, 51, 5, 63, 24, 20, 36, 27, 50, 59, 11, 7, 14, 26, 75, 23, 9, 6, 13, 49, 71, 144, 31, 25, 30, 199, 19, 10, 46, 12, 51, 83, 5, 28, 73, 63, 62, 24, 54, 20, 36, 67, 27, 40, 74, 50, 59, 124 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..75.

EXAMPLE

a(7) = 5 since 7 = 111[2] (i.e. written in base 2) and 5! = 1111000[2] is the least factorial to have 111 as most significant binary digits.

PROG

(PARI) A155891(n)={ local( F=1, k=1 ); while( F\1!=n, F*=k++; while( F>=n+1, F/=2 )); k}

CROSSREFS

Cf. A018799, A076219.

Sequence in context: A092927 A071553 A021812 * A234026 A245443 A246265

Adjacent sequences:  A155888 A155889 A155890 * A155892 A155893 A155894

KEYWORD

base,nonn

AUTHOR

M. F. Hasler, Feb 01 2009

STATUS

approved

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Last modified May 9 10:46 EDT 2021. Contains 343732 sequences. (Running on oeis4.)