1,2

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

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.

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

Cf. A018799, A076219.

Sequence in context: A092927 A071553 A021812 * A234026 A245443 A246265

Adjacent sequences: A155888 A155889 A155890 * A155892 A155893 A155894

base,nonn

M. F. Hasler, Feb 01 2009

approved