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!)
A212541 Let p_n=prime(n), n>=1. Then a(n) is the maximal prime p which differs from p_n, for which the intervals (p/2,p_n/2), (p,p_n], if p<p_n, or the intervals (p_n/2,p/2), (p_n,p], if p>p_n, contain the same number of primes, and a(n)=0, if no such prime p exists. 4
0, 11, 11, 11, 7, 17, 13, 29, 29, 23, 41, 41, 37, 47, 43, 59, 53, 67, 61, 0, 97, 97, 97, 97, 89, 0, 107, 103, 127, 149, 109, 149, 149, 151, 137, 139, 167, 167, 163, 179, 173, 0, 227, 229, 229, 233, 229, 227, 223, 211, 199, 0, 0, 263, 263, 257, 0, 281, 281 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n)<p_n if and only if p_n is Ramanujan prime (A104272).

a(n)=0 if and only if p_n is a peculiar prime, i.e., simultaneously Ramanujan and Labos (A080359) prime (see sequence A164554).

LINKS

Table of n, a(n) for n=1..59.

V. Shevelev, Ramanujan and Labos primes, their generalizations, and classifications of primes, J. Integer Seq. 15 (2012) Article 12.5.4

FORMULA

If p_n is not a Ramanujan prime, then a(n) = A104272(n-pi(p_n/2)).

EXAMPLE

Let n=4, p_n=7. Since 7 is not Ramanujan prime, then a(4) = A104272(4-pi(3.5)) = A104272(2) = 11.

CROSSREFS

Cf. A212493, A104272, A080359, A164554.

Sequence in context: A087380 A152986 A252838 * A087994 A100755 A171902

Adjacent sequences:  A212538 A212539 A212540 * A212542 A212543 A212544

KEYWORD

nonn

AUTHOR

Vladimir Shevelev and Peter J. C. Moses, May 20 2012

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 July 5 17:04 EDT 2020. Contains 335473 sequences. (Running on oeis4.)