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A236386 Numbers n such that phi(n) is an oblong number. 1
3, 4, 6, 7, 9, 13, 14, 18, 21, 25, 26, 28, 31, 33, 36, 42, 43, 44, 49, 50, 62, 66, 73, 86, 87, 91, 95, 98, 111, 116, 117, 121, 135, 146, 148, 152, 157, 161, 169, 174, 182, 190, 201, 207, 211, 216, 222, 228, 234, 237, 241, 242, 252, 268, 270, 287, 289, 305 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

An oblong number (A002378) is of the form k(k+1) where k is a natural number.

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..10000

EXAMPLE

phi(13) = 12 = 3*4, an oblong number; so 13 is a term of the sequence.

MATHEMATICA

Select[Range[500], IntegerQ@Sqrt[1 + 4*EulerPhi[#]] &] (* Giovanni Resta, Jan 24 2014 *)

CROSSREFS

Cf. A000010, A002378.

Sequence in context: A089038 A137673 A226245 * A066271 A127594 A094604

Adjacent sequences:  A236383 A236384 A236385 * A236387 A236388 A236389

KEYWORD

nonn,easy

AUTHOR

Joseph L. Pe, Jan 24 2014

EXTENSIONS

a(16)-a(58) from Giovanni Resta, Jan 24 2014

STATUS

approved

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Last modified February 23 18:54 EST 2018. Contains 299586 sequences. (Running on oeis4.)