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A289275 Numbers k such that the deficiency of k^2 is itself a square. 4
1, 2, 4, 8, 16, 32, 46, 64, 128, 256, 284, 512, 1024, 1633, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 149728, 242656, 260495, 262144, 298057, 524288, 1048576, 1056752, 2097152, 4194304, 8388608, 9587584, 16777216, 17706256, 33554432, 67108864, 134217728 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
The sequence of square roots of the deficiencies of this sequence is A288145.
The current sequence is the disjoint union of the powers of 2 (A000079) and the sequence A289274.
LINKS
MATHEMATICA
Select[Range[10^5], IntegerQ@ Sqrt[2 #^2 - DivisorSigma[1, #^2]] &] (* Michael De Vlieger, Jul 04 2017 *)
PROG
(PARI) isok(n) = issquare(2*n^2 - sigma(n^2)); \\ Michel Marcus, Jul 01 2017
CROSSREFS
Disjoint union of the sequences A000079 and A289274.
Square roots of deficiencies of squares is A288145.
Sequence in context: A133408 A335019 A337719 * A316758 A316750 A008382
KEYWORD
nonn
AUTHOR
Jens Voß, Jun 30 2017
EXTENSIONS
a(35)-a(38) from Giovanni Resta, Jul 27 2017
STATUS
approved

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Last modified March 18 22:56 EDT 2024. Contains 370952 sequences. (Running on oeis4.)