A015883 -id:A015883 - cp's OEIS frontend

A015881 Numbers k such that sigma(k) = sigma(k+11).

28, 154, 466, 874, 958, 1054, 2266, 2878, 11505, 12754, 14674, 17974, 21154, 21778, 29223, 29535, 31725, 32714, 39658, 43186, 48004, 52018, 62338, 70198, 126795, 132783, 163251, 164818, 207603, 212938, 221595, 272685, 274527

Offset: 1

Robert G. Wilson v

nonn

Donovan Johnson, Table of n, a(n) for n = 1..1000

Cf. A002961, A007373, A015861, A015863, A015865, A015866, A015867, A015876, A015877, A015880, A015882, A015883, A181647.

Select[Range[300000], DivisorSigma[1, #]==DivisorSigma[1, # + 11] &] (* Vincenzo Librandi, Mar 10 2014 *)
Position[Partition[DivisorSigma[1,Range[300000]],12,1],?(First[#]== Last[#]&), 1,Heads->False]//Flatten (* _Harvey P. Dale, Aug 20 2017 *)

is(n)=sigma(n)==sigma(n+11) \\ Charles R Greathouse IV, Mar 09 2014

A015882 Numbers k such that sigma(k) = sigma(k+12).

Original entry on oeis.org

35, 104, 285, 287, 310, 329, 340, 345, 406, 609, 660, 736, 767, 957, 1067, 1207, 1242, 1768, 1786, 1817, 1824, 2047, 2288, 2407, 2672, 2686, 2714, 3009, 4012, 4387, 4653, 4847, 6179, 7532, 8366, 8920, 10005, 10528, 11140, 11670, 11951

Offset: 1

Robert G. Wilson v

nonn

Donovan Johnson, Table of n, a(n) for n = 1..1000
A. Weingartner, On the Solutions of sigma(n) = sigma(n+k), Journal of Integer Sequences, Vol. 14 (2011), #11.5.5.

Cf. A002961, A007373, A015861, A015863, A015865, A015866, A015867, A015876, A015877, A015880, A015881, A015883, A181647.

Select[Range[20000], DivisorSigma[1, #]==DivisorSigma[1, # + 12] &] (* Vincenzo Librandi, Mar 10 2014 *)

is(n)=sigma(n)==sigma(n+12) \\ Charles R Greathouse IV, Mar 09 2014

A181647 Numbers m having the same sum of divisors as m+20 has.

Original entry on oeis.org

42, 51, 123, 141, 204, 371, 497, 708, 923, 992, 1034, 1343, 1391, 1484, 1595, 1691, 1826, 3266, 3317, 5015, 5152, 7367, 8003, 9132, 9287, 9494, 11078, 13223, 15458, 15833, 17975, 18752, 19428, 20120, 20915, 21251, 21566, 24119, 24503, 25787, 28000, 29726, 29795

Offset: 1

Reinhard Zumkeller, Nov 03 2010

nonn

			a(1) = 42, divisors(42) = {1,2,3,6,7,14,21,42}, divisors(42+20) = {1,2,31,62}: 1+2+3+6+7+14+21+42 = 1+2+31+62.

Jean-Marie De Koninck, Those Fascinating Numbers, Amer. Math. Soc., 2009, page 16.

Donovan Johnson, Table of n, a(n) for n = 1..1000 (first 100 terms from Reinhard Zumkeller)
Andreas Weingartner, On the Solutions of sigma(n) = sigma(n+k), Journal of Integer Sequences, Vol. 14 (2011), Article 11.5.5.

Cf. A000203, A002961, A007373, A015861, A015863, A015865, A015866, A015867, A015876, A015877, A015880, A015881, A015882, A015883.

Select[Range[30000], Equal @@ DivisorSigma[1, # + {0, 20}] &] (* Amiram Eldar, Apr 16 2025 *)

isok(n) = sigma(n) == sigma(n+20); \\ Michel Marcus, Feb 06 2016

A000203(a(n)) = A000203(a(n) + 20).

A321023 Numbers k such that sigma(k) = sigma(k + 15).

Original entry on oeis.org

26, 62, 20840574, 25741470, 60765690, 102435795, 277471467, 361466454, 464465910, 1110512403, 1927430490, 2741174163, 3631266639, 3844534602, 3982743750, 4565968407, 4612184562, 4829319495, 4981969978, 7066794735, 13484870399, 14268004443, 14550390855, 15051147111

Offset: 1

Tomohiro Yamada, Oct 26 2018

nonn

			sigma(26) = sigma(41) = 42, sigma(62) = sigma(77) = 96.

Giovanni Resta, Table of n, a(n) for n = 1..116 (terms < 2.5*10^12)

Cf. A002961, A007373, A015861, A015863, A015865, A015866, A015867, A015876, A015877, A015880, A015881, A015882, A015883, A172335, A181647, A172333.

my(V=vector(15)); for(n=1, 2^28, my(s=sigma(n), r=(n%15)+1); if (s==V[r], print1(n-15, ", ")); V[r]=s)

a(7)-a(9) from Amiram Eldar, Oct 26 2018

a(10)-a(24) from Giovanni Resta, Oct 26 2018

cp's OEIS Frontend

A015881 Numbers k such that sigma(k) = sigma(k+11).

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A015882 Numbers k such that sigma(k) = sigma(k+12).

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A181647 Numbers m having the same sum of divisors as m+20 has.

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A321023 Numbers k such that sigma(k) = sigma(k + 15).

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