A131378 Starting with 0, the sequence a(n) changes from 0 to 1 or back when the next number n is a prime.

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

Offset

0,1

Comments

Zero together with A071986. - Omar E. Pol, Feb 19 2011

Parity of A230980. - Omar E. Pol, Jul 19 2019

Links

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

Example

n = 0, 1, 2, 3, 4, 5, etc.
a(n)= 0, 0, 1, 0, 0, 1, etc.
Starting with 0 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:=0; 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);

Mathematica

nxt[{n_, a_}]:={n+1, Which[a==0&&PrimeQ[n+1], 1, a==1&&PrimeQ[n+1], 0, True, a]}; NestList[nxt, {0, 0}, 100][[All, 2]] (* Harvey P. Dale, Jul 19 2019 *)

Crossrefs

Cf. A131377.

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

Sequence in context: A189632 A364251 A365421 * A354029 A189624 A014707

Adjacent sequences: A131375 A131376 A131377 * A131379 A131380 A131381

Keyword

easy,nonn

Author

Paolo P. Lava and Giorgio Balzarotti, Jul 04 2007

Status

approved