A323162 a(n) = 1 if both n and n-1 are composite, 0 otherwise.

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

Offset

1

Comments

Characteristic function of A005381.

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for characteristic functions

Formula

a(1) = 0; for n > 1, a(n) = (1-A010051(n-1)) * (1-A010051(n)).

a(A005381(n)) = 1, a(A093515(n)) = 0.

For n >= 4, a(n) = 1-A090405(n-2).

Mathematica

Map[Boole[AllTrue[#, CompositeQ]] &, Partition[Range[0, 120], 2, 1]] (* Michael De Vlieger, Jan 07 2019 *)

Prog

(PARI) A323162(n) = ((n>1)&&(!isprime(n))&&(!isprime(n-1)));

Crossrefs

Cf. A005381, A010051, A090405, A093515, A323161.

Sequence in context: A373266 A276404 A277153 * A185017 A359472 A295883

Adjacent sequences: A323159 A323160 A323161 * A323163 A323164 A323165

Keyword

nonn

Author

Antti Karttunen, Jan 07 2019

Status

approved