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A172333 Numbers m such that m and m+22 have the same sum of divisors. 2
57, 85, 213, 224, 354, 476, 568, 594, 812, 1218, 1235, 1316, 1484, 2103, 2470, 2492, 2643, 2840, 2996, 3836, 3978, 4026, 4544, 4810, 4844, 5012, 6125, 6356, 6524, 7364, 7532, 7648, 8876, 9272, 9328, 10098, 11107, 11797, 12572, 12594, 13412, 13640 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If 3*k-1 and 14*k-1 are both prime with k>1, then n = 28*(3*k-1) belongs to this sequence. The number of such integers n <= x would be asymptotically cx/(log x)^2 for some constant c > 0 from the Hardy-Littlewood conjecture D in Partitio Numerorum. - Tomohiro Yamada, Oct 03 2018

REFERENCES

J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 62, p. 22, Ellipses, Paris 2008.

W. Sierpinski, A Selection of Problems in the Theory of Numbers. Macmillan, NY, 1964, p. 110.

Tomohiro Yamada, On equations sigma(n) = sigma(n+k) and phi(n) = phi(n+k), J. Comb. Number Theory 9 (2017), 15-21.

LINKS

Tomohiro Yamada, Table of n, a(n) for n = 1..46702 (All terms < 2^28, first 2000 terms from Muniru A Asiru)

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972.

G. H. Hardy and J. E. Littlewood, Some problems of 'Partitio numerorum'; III: On the expression of a number as a sum of primes, Acta Math. 44 (1923), 1-70.

Tomohiro Yamada, On equations sigma(n) = sigma(n+k) and phi(n) = phi(n+k)<, arXiv:1001.2511 [math.NT], 2010.

MAPLE

with(numtheory):for n from 1 to 20000 do; if sigma(n) = sigma(n+22) then print(n); else fi ; od;

PROG

(PARI) isok(k) = sigma(k)==sigma(k+22); \\ Altug Alkan, Oct 03 2018

(GAP) Filtered([1..13700], k->Sigma(k)=Sigma(k+22)); # Muniru A Asiru, Oct 20 2018

CROSSREFS

Cf. A000203, A015861, A002961, A015865, A015867, A015858, A015859, A015860.

Sequence in context: A087921 A196580 A086097 * A200932 A145554 A111320

Adjacent sequences:  A172330 A172331 A172332 * A172334 A172335 A172336

KEYWORD

nonn

AUTHOR

Michel Lagneau, Feb 01 2010

STATUS

approved

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Last modified May 15 06:18 EDT 2021. Contains 343909 sequences. (Running on oeis4.)