The On-Line Encyclopedia of Integer Sequences (OEIS)

Revisions by Chai Wah Wu

(See also Chai Wah Wu's wiki page)

(Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
Showing entries 1-10 | older changes

A075084

Number of composite numbers c with n <= c <= 2*n.
(history; published version)

#17 by Chai Wah Wu at Sun Oct 20 22:09:45 EDT 2024

STATUS

editing

proposed

#16 by Chai Wah Wu at Sun Oct 20 22:09:40 EDT 2024

PROG

(Python)

from sympy import primepi

def A075084(n): return n+primepi(n-1)-primepi(n<<1)+1 if n>1 else 0 # Chai Wah Wu, Oct 20 2024

STATUS

approved

editing

A307912

a(n) = n - 1 - pi(2*n-1) + pi(n), where pi is the prime counting function.
(history; published version)

#41 by Chai Wah Wu at Sun Oct 20 19:30:51 EDT 2024

STATUS

editing

proposed

#40 by Chai Wah Wu at Sun Oct 20 19:30:48 EDT 2024

PROG

(Python)

from sympy import primepi

def A307912(n): return n+primepi(n)-primepi((n<<1)-1)-1 # Chai Wah Wu, Oct 20 2024

STATUS

approved

editing

A307989

a(n) = n - pi(2*n) + pi(n-1), where pi is the prime counting function.
(history; published version)

#7 by Chai Wah Wu at Sun Oct 20 19:29:10 EDT 2024

STATUS

editing

proposed

#6 by Chai Wah Wu at Sun Oct 20 19:29:02 EDT 2024

PROG

(Python)

from sympy import primepi

def A307989(n): return n+primepi(n-1)-primepi(n<<1) # Chai Wah Wu, Oct 20 2024

STATUS

approved

editing

A376759

Number of composite numbers c with n < c <= 2*n.
(history; published version)

#5 by Chai Wah Wu at Sun Oct 20 19:27:23 EDT 2024

STATUS

editing

proposed

#4 by Chai Wah Wu at Sun Oct 20 19:27:16 EDT 2024

PROG

(Python)

from sympy import primepi

def A376759(n): return n+primepi(n)-primepi(n<<1) # Chai Wah Wu, Oct 20 2024

STATUS

approved

editing

A377212

a(n) is the least number k that is not a quadratic residue modulo prime(n) but is a quadratic residue modulo all previous primes.
(history; published version)

#15 by Chai Wah Wu at Sun Oct 20 17:22:04 EDT 2024

STATUS

editing

proposed

#14 by Chai Wah Wu at Sun Oct 20 17:21:51 EDT 2024

PROG

if q>p or legendre_symbol(k, q)==-1:

STATUS

proposed

editing