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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A230774 Number of primes less than first prime above square root of n. 2
 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS Or repeat k (prime(k)^2 - prime(k-1)^2) times, with prime(0) set to 0 for k = 1. This sequence is useful to compute A055399 for prime numbers. LINKS Jean-Christophe Hervé, Table of n, a(n) for n = 1..10000 FORMULA Repeat 1 prime(1)^2 = 4 times; for k>1, repeat k (prime(k)^2-prime(k-1)^2) = A050216(k-1) times. a(n) - A056811(n) = characteristic function of squares of primes. EXAMPLE a(5) = a(6) = a(7) = a(8) = a(9) = 2 because prime(1) = 2 < sqrt(5 to 9) <= prime(2) = 3. MATHEMATICA Table[1 + PrimePi[Sqrt[n-1]], {n, 100}] (* Alonso del Arte, Nov 01 2013 *) CROSSREFS Cf. A050216, A056811, A055399, A230775. Sequence in context: A319816 A343437 A105517 * A056813 A125269 A077430 Adjacent sequences:  A230771 A230772 A230773 * A230775 A230776 A230777 KEYWORD nonn,easy AUTHOR Jean-Christophe Hervé, Nov 01 2013 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.

Last modified June 22 19:48 EDT 2021. Contains 345388 sequences. (Running on oeis4.)