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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A090970 Number of primes strictly between T(n) and T(n+1), where T(n) = n-th triangular number. 4
1, 1, 1, 2, 2, 1, 2, 3, 2, 2, 3, 3, 3, 3, 2, 4, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 6, 4, 5, 3, 6, 6, 7, 5, 5, 6, 4, 8, 5, 6, 6, 8, 6, 8, 5, 7, 5, 11, 4, 6, 9, 7, 8, 9, 8, 7, 7, 9, 7, 8, 7, 12, 5, 9, 9, 11, 9, 7, 7, 12, 10, 10, 9, 9, 9, 6, 11, 10, 11, 9, 12, 11, 12, 9, 10, 11, 12, 10, 13, 9, 11, 10, 12 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

EXAMPLE

a(8)=3 because between T(8)=36 and T(9)=45 we have the prime numbers 37,41 and 43.

MAPLE

a:= proc(n) local ct, j: ct:=0: for j from n*(n+1)/2+1 to (n+1)*(n+2)/2-1 do if isprime(j)=true then ct:=ct+1 else ct:=ct fi: od: end: seq(a(n), n=1..103); # Emeric Deutsch, Feb 23 2005

MATHEMATICA

With[{trs=Partition[Accumulate[Range[100]], 2, 1]}, Join[{1}, Rest[ PrimePi[ #[[2]]]- PrimePi[#[[1]]]&/@trs]]] (* Harvey P. Dale, Aug 25 2015 *)

CROSSREFS

Essentially the same as A065382 and A066888.

Sequence in context: A238325 A238885 A023566 * A091972 A025833 A200647

Adjacent sequences:  A090967 A090968 A090969 * A090971 A090972 A090973

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Jan 03 2004

EXTENSIONS

More terms from Emeric Deutsch, Feb 23 2005

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 August 24 18:12 EDT 2019. Contains 326295 sequences. (Running on oeis4.)