A181647 -id:A181647 - 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

A015883 Numbers k such that sigma(k) = sigma(k+13).

Original entry on oeis.org

182, 782, 1965, 2486, 2678, 2685, 12141, 12441, 17342, 21242, 27686, 34905, 35505, 35853, 38662, 38985, 56732, 63578, 104342, 109461, 192933, 198909, 222122, 236966, 245349, 251654, 256322, 261885, 262238, 324441, 333909

Offset: 1

Robert G. Wilson v

nonn

J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 182, p. 56, Ellipses, Paris 2008.

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

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

Select[Range[350000], DivisorSigma[1, #]==DivisorSigma[1, # + 13] &] (* Vincenzo Librandi, Mar 10 2014 *)

is(n)=sigma(n)==sigma(n+13) \\ Charles R Greathouse IV, Mar 09 2014

Corrected by T. D. Noe, Oct 31 2006

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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A015883 Numbers k such that sigma(k) = sigma(k+13).

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

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