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A073783 First differences of composite numbers. 9
2, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 2, 1, 1, 2, 2, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 2, 2, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also, the highest common factors of pair of successive composite numbers. - Amarnath Murthy, Jan 31 2003

A073783(n) = A073784(n) + 1.

All terms are 1 or 2. Runs of 1's may be of arbitrary lengths, while the lengths of runs of 2's are 1 or 2.  - Zak Seidov, Mar 18 2013

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A002808(n+1) - A002808(n).

EXAMPLE

a(7) = A002808(8) - A002808(7) = 15 - 14 = 1.

MATHEMATICA

c[x_] := FixedPoint[x + PrimePi[#] + 1 &, x]; Differences[c /@ Range[106]] (* Jayanta Basu, Jul 09 2013 *)

PROG

(Haskell)

a073783 n = a073783_list !! (n-1)

a073783_list = zipWith (-) (tail a002808_list) a002808_list

-- Reinhard Zumkeller, Jan 10 2013

(PARI) m=4; forcomposite(n=6, 1e3, print1(n-m", "); m=n) \\ Charles R Greathouse IV, Mar 20 2013

CROSSREFS

Cf. A002808, A073784.

a(n) = A136527(n, n+1).

Cf. A073445 (first differences).

Sequence in context: A286944 A026605 A270646 * A134430 A130658 A014695

Adjacent sequences:  A073780 A073781 A073782 * A073784 A073785 A073786

KEYWORD

easy,nonn

AUTHOR

Lior Manor Aug 11 2002

STATUS

approved

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Last modified July 21 04:27 EDT 2017. Contains 289632 sequences.