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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: A275589 A129808 A330384 * A308375 A329423 A132025

Adjacent sequences:  A077646 A077647 A077648 * A077650 A077651 A077652

KEYWORD

base,easy,nonn

AUTHOR

Labos Elemer, Nov 19 2002

STATUS

approved

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Last modified September 27 08:39 EDT 2021. Contains 347689 sequences. (Running on oeis4.)