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A003502 The smaller of a betrothed pair. 9
48, 140, 1050, 1575, 2024, 5775, 8892, 9504, 62744, 186615, 196664, 199760, 266000, 312620, 526575, 573560, 587460, 1000824, 1081184, 1139144, 1140020, 1173704, 1208504, 1233056, 1236536, 1279950, 1921185, 2036420, 2102750, 2140215, 2171240, 2198504, 2312024 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

R. K. Guy, Unsolved Problems in Number Theory, B5.

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..4122 (terms < 10^13, terms 1..1000 from Donovan Johnson, 1001..1126 from Amiram Eldar)

P. Hagis and G. Lord, Quasi-amicable numbers, Math. Comp. 31 (1977), 608-611.

D. Moews, Augmented amicable pairs

Jan Munch Pedersen, Tables of Aliquot Cycles

Wikipedia, Betrothed numbers

EXAMPLE

48 is a term because sigma(48) - 48 - 1 = 124 - 48 - 1 = 75 and 48 < 75 and sigma(75) - 75 - 1 = 124 - 75 - 1 = 48. - David A. Corneth, Jan 24 2019

MATHEMATICA

aapQ[n_] := Module[{c=DivisorSigma[1, n]-1-n}, c!=n&&DivisorSigma[ 1, c]-1-c == n]; Transpose[Union[Sort[{#, DivisorSigma[1, #]-1-#}]&/@Select[Range[2, 10000], aapQ]]] [[1]] (* Amiram Eldar, Jan 24 2019 after Harvey P. Dale at A007992 *)

PROG

(PARI) is(n) = m = sigma(n) - n - 1; if(m == 0 || n >= m, return(0)); n == sigma(m) - m - 1 \\ David A. Corneth, Jan 24 2019

CROSSREFS

Cf. A000203, A003503, A005276.

Sequence in context: A260972 A244380 A260493 * A129428 A039496 A044380

Adjacent sequences:  A003499 A003500 A003501 * A003503 A003504 A003505

KEYWORD

nonn,nice

AUTHOR

Robert G. Wilson v

EXTENSIONS

Computed by Fred W. Helenius (fredh(AT)ix.netcom.com)

Extended by T. D. Noe, Dec 29 2011

STATUS

approved

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Last modified February 23 12:38 EST 2020. Contains 332159 sequences. (Running on oeis4.)