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A111208 Number of primes <= n-th triangular number. +0
1
0, 0, 2, 3, 4, 6, 8, 9, 11, 14, 16, 18, 21, 24, 27, 30, 32, 36, 39, 42, 46, 50, 54, 58, 62, 66, 70, 74, 79, 84, 90, 94, 99, 102, 108, 114, 121, 126, 131, 137, 141, 149, 154, 160, 166, 174, 180, 188, 193, 200, 205, 216, 220, 226, 235, 242, 250, 259, 267, 274, 281, 290 (list; graph; listen)
OFFSET

0,3

COMMENT

Only because of the case n = 2 is it necessary to say "<=", otherwise "<" would suffice. Except for the first two terms, there are no consecutive identical terms for n < 10000. A065382 gives differences between consecutive terms of this sequence. - Alonso Delarte (alonso.delarte(AT)gmail.com), Oct 31 2005

FORMULA

a(n) = A000720(A000217(n)).

MATHEMATICA

Table[PrimePi[n*(n + 1)/2], {n, 0, 60}] (*Chandler*)

CROSSREFS

Cf. A000720, A000217.

Sequence in context: A018649 A135676 A102701 this_sequence A085500 A010385 A095037

Adjacent sequences: A111205 A111206 A111207 this_sequence A111209 A111210 A111211

KEYWORD

nonn

AUTHOR

Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Oct 25 2005

EXTENSIONS

Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net) and Alonso Delarte (alonso.delarte(AT)gmail.com), Oct 31 2005

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Last modified July 26 13:41 EDT 2008. Contains 142293 sequences.


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