This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A182434 Number of primes p < n such that 4*p+1 is also prime. 2
 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 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, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,7 LINKS Enrique Pérez Herrero, Table of n, a(n) for n = 1..10000 FORMULA a(10^n) = A182265(n). a(n) = sum(i=2..n, floor(phi(4*i^2+i)/(4*i^2-4*i))). - Enrique Pérez Herrero, May 02 2012. MATHEMATICA Accumulate[Table[Boole[PrimeQ[n]&&PrimeQ[4n+1]], {n, 1, 200}]] Accumulate[If[AllTrue[{#, 4#+1}, PrimeQ], 1, 0]&/@Range[90]] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Feb 26 2015 *) CROSSREFS Cf. A023212, A182265. Cf. A005384, A156660, A156874, A092816. Sequence in context: A208246 A320857 A211664 * A185679 A080342 A081604 Adjacent sequences:  A182431 A182432 A182433 * A182435 A182436 A182437 KEYWORD nonn AUTHOR Enrique Pérez Herrero, Apr 28 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.

Last modified December 7 09:33 EST 2019. Contains 329843 sequences. (Running on oeis4.)