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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
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
KEYWORD
nonn
AUTHOR
STATUS
approved