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A229511 Numbers k whose arithmetic derivative (k') is a triangular number. 1
0, 1, 2, 3, 5, 7, 9, 11, 13, 17, 18, 19, 21, 23, 25, 26, 29, 31, 37, 38, 41, 43, 47, 50, 53, 59, 61, 67, 71, 73, 75, 79, 83, 86, 89, 97, 101, 102, 103, 106, 107, 109, 113, 115, 116, 127, 131, 137, 139, 147, 149, 151, 155, 157, 163, 167, 173, 178, 179, 181, 187, 191, 193, 197, 199 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Paolo P. Lava, Table of n, a(n) for n = 0..1000

EXAMPLE

3 is in the sequence since 3'=1 and 1 is a triangular number.

4 is not in the sequence since 4'=4 and 4 is not a triangular number.

MAPLE

with(numtheory); P:= proc(q) local a, p, n;

for n from 0 to q do a:=n*add(op(2, p)/op(1, p), p=ifactors(n)[2]);

if type((-1+sqrt(1+8*a))/2, integer) then print(n); fi; od; end: P(10^6); # Paolo P. Lava, Sep 25 2013

CROSSREFS

Cf. A000217, A003415.

Sequence in context: A097046 A248420 A011861 * A305078 A328336 A337694

Adjacent sequences:  A229508 A229509 A229510 * A229512 A229513 A229514

KEYWORD

nonn,easy

AUTHOR

Luca Brigada Villa, Sep 25 2013

STATUS

approved

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Last modified October 30 03:11 EDT 2020. Contains 338076 sequences. (Running on oeis4.)