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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 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

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Last modified July 14 16:43 EDT 2024. Contains 374322 sequences. (Running on oeis4.)