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A008507 Number of odd composite numbers less than n-th odd prime. 2
0, 0, 0, 1, 1, 2, 2, 3, 5, 5, 7, 8, 8, 9, 11, 13, 13, 15, 16, 16, 18, 19, 21, 24, 25, 25, 26, 26, 27, 33, 34, 36, 36, 40, 40, 42, 44, 45, 47, 49, 49, 53, 53, 54, 54, 59, 64, 65, 65, 66, 68, 68, 72, 74, 76, 78, 78, 80, 81, 81, 85, 91, 92, 92, 93, 99, 101, 105, 105, 106, 108, 111, 113, 115, 116, 118 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

a(n) = A067076(n) - n + 1. - Vincenzo Librandi, Feb 02 2013

For n>=4, a(n) = k+1, where A000217(j) is the smallest triangular number such that A000217(j) - A033286(n+1) also is a triangular number, i.e., A000217(k). Example n=29, a(29) = 27: A033286(30) = 3390, A000217(86) = 3741. 3741-3390 = 351 = A000217(26); k=26, 26+1 = 27. - Bob Selcoe, Apr 12 2016

LINKS

Table of n, a(n) for n=1..76.

FORMULA

[(Odd Primes - 1)/2] - n for n > 0, or A005097(n) - A000027(n). For example, A005097(1) - A000027(1) = 1 - 1 = 0, A005097(2) - A000027(2) = 2 - 2 = 0, A005097(9) - A000027(9) = 14 - 9 = 5. - William A. Tedeschi, Apr 25 2008

CROSSREFS

Cf. A067076.

Cf. A000040 (prime numbers), A000217 (triangular numbers), A033286 (n*prime(n)).

Sequence in context: A089366 A113827 A033189 * A028364 A239482 A280470

Adjacent sequences:  A008504 A008505 A008506 * A008508 A008509 A008510

KEYWORD

nonn

AUTHOR

Gary Findley (chfindley(AT)alpha.nlu.edu)

EXTENSIONS

More terms from David W. Wilson, Jan 13 2000

STATUS

approved

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Last modified November 21 13:53 EST 2017. Contains 295001 sequences.