A131377 Starting with 1, the sequence a(n) changes from 1 to 0 or back when the next number n is a prime.

1, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0

Offset

0,1

Links

Table of n, a(n) for n=0..100.

Formula

a(n) = 1 - A071986(n).

Example

n = 0, 1, 2, 3, 4, 5, etc..
a(n)= 1, 1, 0, 1, 1, 0, etc.
Starting with 1 the sequence changes when we move from 1 to 2 because 2 is prime, again from 2 to 3 because also 3 is prime, then from 4 to 5 being 5 prime and so on.

Maple

P:=proc(n) local i, k; k:=1; for i from 0 by 1 to n do if isprime(i) then if k=1 then k:=0; else k:=1; fi; fi; print(k); od; end: P(100);

Crossrefs

Cf. A131378.

Cf. A071986. - Omar E. Pol, Feb 19 2011

Sequence in context: A014577 A157926 A263243 * A364639 A342991 A285898

Adjacent sequences: A131374 A131375 A131376 * A131378 A131379 A131380

Keyword

easy,nonn

Author

Paolo P. Lava and Giorgio Balzarotti, Jul 04 2007

Status

approved