A391746 Number of terms of A391909 <= n.

1, 2, 3, 3, 4, 5, 6, 6, 6, 6, 7, 8, 9, 10, 11, 11, 12, 13, 14, 14, 14, 14, 15, 15, 15, 16, 16, 17, 18, 19, 20, 20, 21, 21, 22, 23, 24, 25, 25, 25, 26, 27, 28, 28, 29, 29, 30, 30, 30, 30, 31, 32, 33, 33, 33, 33, 33, 34, 35, 35, 36, 36, 36, 36, 37, 38, 39, 39, 40, 41, 42, 43, 44, 45

Offset

1,2

Links

Antti Karttunen, Table of n, a(n) for n = 1..16384

Index entries for sequences related to prime indices in the factorization of n.

Formula

a(1) = A391747(1), and for n > 1, a(n) = a(n-1) + A391747(n).

Prog

(PARI)
up_to = 16384;
A195017(n) = { my(f); if(1==n, 0, f=factor(n); sum(i=1, #f~, f[i, 2] * (-1)^(1+primepi(f[i, 1])))); };
A391747(n) = (abs(A195017(n)) <= 1);
A391746_list(up_to_n) = { my(v=vector(up_to_n)); v[1] = A391747(1); for(i=2, #v, v[i] = v[i-1]+A391747(i)); (v); };
v391746 = A391746_list(up_to);
A391746(n) = v391746[n];

Crossrefs

Partial sums of A391747, a left inverse of A391909.

Cf. A195017.

Sequence in context: A064047 A335152 A111899 * A074753 A387584 A013928

Adjacent sequences: A391743 A391744 A391745 * A391747 A391748 A391749

Keyword

nonn

Author

Antti Karttunen and Peter Munn, Jan 02 2026

Status

approved