login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A077649 Initial digit of composite numbers. 0
4, 6, 8, 9, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..105.

FORMULA

a(n) = A000030(A002808(n)).

MATHEMATICA

c[x_] := FixedPoint[x+PrimePi[ # ]+1&, x] Table[First[IntegerDigits[c[w]]], {w, 1, 128}]

First[IntegerDigits[#]]&/@Complement[Range[150], Prime[Range[ PrimePi[150]]]]  (* Harvey P. Dale, Apr 26 2011 *)

PROG

(PARI) lista(nn) = forcomposite(n=1, nn, print1(digits(n)[1], ", ")); \\ Michel Marcus, Dec 13 2017

CROSSREFS

Cf. A000030, A002808, A077648.

Sequence in context: A110750 A275589 A129808 * A308375 A132025 A200363

Adjacent sequences:  A077646 A077647 A077648 * A077650 A077651 A077652

KEYWORD

base,easy,nonn

AUTHOR

Labos Elemer, Nov 19 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 11 22:31 EST 2019. Contains 329046 sequences. (Running on oeis4.)