login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A249738 a(n) = 0 if n is 1 or a prime, otherwise, when n = A020639(n) * A032742(n), a(n) = the largest k < A032742(n) such that either k = 1 or A020639(k) >= A020639(n), where A020639(n) and A032742(n) are the smallest prime and the largest proper divisor dividing n. 3
0, 0, 0, 1, 0, 2, 0, 3, 1, 4, 0, 5, 0, 6, 3, 7, 0, 8, 0, 9, 5, 10, 0, 11, 1, 12, 7, 13, 0, 14, 0, 15, 9, 16, 5, 17, 0, 18, 11, 19, 0, 20, 0, 21, 13, 22, 0, 23, 1, 24, 15, 25, 0, 26, 7, 27, 17, 28, 0, 29, 0, 30, 19, 31, 11, 32, 0, 33, 21, 34, 0, 35, 0, 36, 23, 37, 7, 38, 0, 39, 25, 40, 0, 41, 13, 42, 27, 43, 0, 44, 11, 45, 29, 46, 17, 47, 0, 48, 31, 49, 0, 50 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

FORMULA

Other identities:

a(n) = A249744(n) / A020639(n).

a(k) = 1 if and only if k is one of A001248 (squares of primes).

PROG

(Scheme) (define (A249738 n) (cond ((or (= 1 n) (prime? n)) 0) (else (let ((lpf (A020639 n))) (let loop ((k (- (A032742 n) 1))) (cond ((= 1 k) k) ((>= (A020639 k) lpf) k) (else (loop (- k 1)))))))))

CROSSREFS

Cf. A020639, A032742, A078898, A249744.

Sequence in context: A241917 A243056 A279119 * A110514 A249122 A135157

Adjacent sequences:  A249735 A249736 A249737 * A249739 A249740 A249741

KEYWORD

nonn

AUTHOR

Antti Karttunen, Dec 06 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 7 02:08 EDT 2020. Contains 333292 sequences. (Running on oeis4.)