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 A220492 Number of primes p between quarter-squares, Q(n) < p <= Q(n+1), where Q(n) = A002620(n). 4
 0, 0, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 2, 2, 2, 2, 1, 4, 1, 2, 2, 2, 3, 3, 2, 2, 2, 4, 2, 4, 3, 1, 4, 2, 4, 3, 3, 3, 4, 4, 3, 4, 3, 2, 4, 4, 5, 4, 4, 4, 3, 4, 4, 4, 5, 4, 4, 4, 4, 5, 5, 5, 4, 6, 4, 4, 5, 5, 5, 7, 2, 3, 6, 6, 6, 6, 5, 8, 4, 5, 6, 5, 4, 7 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,9 COMMENTS It appears that a(n) > 0, if n > 1. Apparently the above comment is equivalent to the Oppermann's conjecture. - Omar E. Pol, Oct 26 2013 LINKS Wikipedia, Oppermann's conjecture EXAMPLE When the nonnegative integers are written as an irregular triangle in which the right border gives the quarter-squares without repetitions, a(n) is the number of primes in the n-th row of triangle. See below (note that the prime numbers are in parenthesis): --------------------------------------- Triangle                          a(n) --------------------------------------- 0;                                 0 1;                                 0 (2);                               1 (3),   4;                          1 (5),   6;                          1 (7),   8,   9;                     1 10,  (11), 12;                     1 (13), 14,  15,   16;               1 (17), 18, (19),  20;               2 21,   22, (23),  24,  25;          1 26,   27,  28,  (29), 30;          1 ... CROSSREFS Partial sums give A220506. Cf. A000040, A002620, A001477, A014085, A066888, A073882, A222030. Sequence in context: A037226 A089641 A086995 * A229873 A135230 A117957 Adjacent sequences:  A220489 A220490 A220491 * A220493 A220494 A220495 KEYWORD nonn AUTHOR Omar E. Pol, Feb 04 2013 STATUS approved

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Last modified October 19 09:28 EDT 2018. Contains 316339 sequences. (Running on oeis4.)