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

Author

Labos Elemer, Nov 19 2002

Keywords

• base
• easy
• nonn

Crossrefs

Cf. A000030, A002808, A077648.

Programs

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 *)

PARI

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

Formula

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