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A172433
Let u(n) = Sum [n/[sqrt k]] and v(n) = Sum [n/(sqrt k)] where the summation index k ranges from 1 to infinity, although both sums are actually finite. Here [a] denotes the integer part of a. Then a(n) = u(n) - v(n).
0
2, 6, 9, 16, 17, 27, 26, 36, 38, 48, 43, 67, 59, 67, 72, 88, 75, 102, 86, 111, 115, 123, 99, 150, 137, 142, 139, 169, 141, 192, 166, 192, 186, 189, 176, 253, 214, 217, 207, 263, 223, 284, 239, 269, 285, 285, 230, 332, 294, 325, 305, 339, 282, 350, 324, 391, 370, 369, 300, 448, 382, 377, 385, 438, 400
OFFSET
1,1
COMMENTS
One can pick out the values of the sequence at primes, obtaining the new sequence 6,9,17,26,43,59,75,86,99,141 which seems to be monotone, unlike the original sequence.
Actually, the infinite sum can be replaced by a finite sum with terms up to (n+1)^2 (see second PARI script). Apparently v(n) is A153818(n). - Michel Marcus, Jul 17 2013
PROG
(PARI) a(n) = round(suminf(k=1, floor(n/sqrtint(k))) - suminf(k=1, floor(n/sqrt(k)))) \\ Michel Marcus, Jul 17 2013
(PARI) a(n) = sum(k=1, (n+1)^2, floor(n/sqrtint(k))) - sum(k=1, (n+1)^2, floor(n/sqrt(k))) \\ Michel Marcus, Jul 17 2013
CROSSREFS
Sequence in context: A355738 A329743 A320496 * A049622 A043548 A347535
KEYWORD
nonn
AUTHOR
Ali A. Tanara (aatanara(AT)gmail.com), Feb 02 2010
EXTENSIONS
Definition clarified by Gihan Marasingha (G_Marasingha(AT)hotmail.com), Feb 10 2010
STATUS
approved