A155891 Least positive integer such that a(n)! starts with n, both written in binary.

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

Offset

1,2

Links

Nick Hobson, Table of n, a(n) for n = 1..16383

Nick Hobson, C program.

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 its 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}
(C) See Links section.

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