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A280682 Integers m such that floor(sqrt(m)) is even. 1
0, 4, 5, 6, 7, 8, 16, 17, 18, 19, 20, 21, 22, 23, 24, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also integers m such that Sum_{k=1..m} floor(k/m) is even (cf. A006218). See the Mathematical Reflections link.

This sequence is composed of blocks of 1,5,9,13,... (A016813:4n+1) consecutive terms, separated by 3,7,11,15,... (A004767:4n+3) consecutive terms.

LINKS

Michel Marcus, Table of n, a(n) for n = 1..4950

Mathematical Reflections, Solution to Problem O349, Issue 6, 2015, p. 19.

EXAMPLE

3 whose sqrt is 1.732... does not belong to this sequence.

5 whose sqrt is 2.236... belongs to this sequence.

PROG

(PARI) isok(n) = (sqrtint(n) % 2) == 0; \\ Michel Marcus, Jan 07 2017

CROSSREFS

Cf. A000196, A006218, A004767, A016813.

Sequence in context: A059709 A071623 A274552 * A140293 A075341 A309358

Adjacent sequences:  A280679 A280680 A280681 * A280683 A280684 A280685

KEYWORD

nonn,easy

AUTHOR

Michel Marcus, Jan 07 2017

STATUS

approved

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Last modified February 17 00:49 EST 2020. Contains 331976 sequences. (Running on oeis4.)