A373497 If n is prime, a(n) = 1 if the number of steps in its prime index chain is odd, a(n) = -1 if the number of steps is even, and a(n) = 0 is n is composite or 1.

0, 1, -1, 0, 1, 0, 1, 0, 0, 0, -1, 0, 1, 0, 0, 0, -1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, -1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, -1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, -1, 0, 0, 0, 0, 0, 1, 0

Offset

1,1

Links

Table of n, a(n) for n=1..90.

Formula

a(n) = 1 iff n is in A333242.

a(n) = -1 iff n is in A262275.

a(n) = 0 iff n is in A018252.

Prog

(PARI) b(n)={my(k=0); while(isprime(n), k++; n=primepi(n)); k}; \\ A078442
a(n) = if ((n==1) || !isprime(n), return(0)); if (b(n)%2, 1, -1); \\ Michel Marcus, Jun 11 2024

Crossrefs

Cf. A333242, A262275, A018252.

Sequence in context: A122257 A332219 A227625 * A129950 A010051 A358751

Adjacent sequences: A373494 A373495 A373496 * A373498 A373499 A373500

Keyword

sign

Author

Michael P. May, Jun 06 2024

Extensions

More terms from Michel Marcus, Jun 11 2024

Status

approved