A077649 Initial digit of composite numbers.

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

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