login
This site is supported by donations to The OEIS Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A246792 Smallest number m such that for 0 < k < n+1, np(m+k-1) = np(m)-k+1, where np(t) is number of primes p with prime(t) < p < prime(t)^(1 + 1/t). 3
1, 7, 25, 25, 181, 208, 208, 1867, 14345, 19609, 40918, 40918, 620326, 2552265, 2552265, 7225612, 7225612, 16679492, 33772734, 33772734, 33772734, 620326386, 1516416904, 1516416904, 4764006481, 5272314878, 21423652192 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

np(m) = A182134(m).

According to the definition, numbers np(a(n)), np(a(n)+1), ..., np(a(n)+n-2) and np(a(n)+n-1) are n consecutive numbers in descending order.

a(34) > 10^12. - Robert Price, Dec 07 2014

See A251736 for the corresponding values of np.

LINKS

Robert Price, Table of n, a(n) for n = 1..33

EXAMPLE

a(15) = 2552265, since np(2552265) = 24, np(2552265+1) = 23 , ..., np(2552265+13) = 11, np(2552265+14) = 10 are 15 consecutive numbers in descending order.

MATHEMATICA

np[t_] := np[t] = Length[Select[Range[Prime[t]+1, Prime[t]^(1+1/t)], PrimeQ]]; a[1]=1; a[n_] := a[n] = (For[m = a[n-1], c = Table[np[m+k-1], {k, n}]; c !=  Reverse[Range[Min[c], Max[c]]], m++]; m); Do[Print[a[n]], {n, 15}]

PROG

(PARI) np(n) = primepi(prime(n)^(1+1/n))-n;

isok(m, n) = {for (k=1, n, if (np(m+k-1) != np(m)-k+1, return (0)); ); return (1); }

a(n) = {m = 1; while (! isok(m, n), m++); m; } \\ Michel Marcus, Dec 07 2014

CROSSREFS

Cf. A000040, A182134, A246791, A251736.

Sequence in context: A065658 A242322 A249437 * A178370 A034125 A196013

Adjacent sequences:  A246789 A246790 A246791 * A246793 A246794 A246795

KEYWORD

nonn

AUTHOR

Farideh Firoozbakht, Oct 16 2014

EXTENSIONS

a(18)-a(33) from Robert Price, Dec 07 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 January 16 03:55 EST 2019. Contains 319184 sequences. (Running on oeis4.)