A118663 Index of the least prime dividing the n-th composite number: A000720(A020639(A002808(n))).

1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 3, 1, 2, 1, 1, 1, 2, 1, 3, 1, 1, 2, 1, 1, 1, 2, 1, 1, 4, 1, 2, 1, 1, 3, 1, 2, 1, 1, 1, 2, 1, 3, 1, 1, 2, 1, 1, 1, 2, 1, 4, 1, 1, 2, 1, 1, 3, 1, 2, 1, 1, 4, 1, 2, 1, 3, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 3, 1, 2, 1, 4, 1, 5, 1, 2, 1, 3, 1, 1, 2, 1, 1, 4, 1, 2, 1, 1, 1, 2

Offset

1,4

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Formula

A118663 = A000720 o A056608. - M. F. Hasler, Apr 03 2012

Mathematica

PrimePi[FactorInteger[#][[1, 1]]]&/@Select[Range[200], CompositeQ] (* Harvey P. Dale, May 13 2023 *)

Prog

(PARI) for(i=2, 999, isprime(i)||print1(primepi(factor(i)[1, 1])", ")) \\ - M. F. Hasler, Apr 03 2012

Crossrefs

Cf. A056608.

Sequence in context: A341997 A053543 A161099 * A205119 A355150 A333915

Adjacent sequences: A118660 A118661 A118662 * A118664 A118665 A118666

Keyword

easy,nonn

Author

Giovanni Teofilatto, May 19 2006

Status

approved