A067130 -id:A067130 - cp's OEIS frontend

A227304 Numbers k such that sigma(k+1) divides sigma(k-1).

34, 55, 285, 367, 835, 849, 919, 1241, 1505, 2911, 2914, 3305, 4149, 4188, 6111, 6903, 7170, 7913, 8506, 9360, 10251, 10541, 12566, 15086, 17273, 17815, 19005, 19689, 21411, 21462, 24882, 25020, 25501, 26610, 28125, 30361, 30593, 30789, 31485, 37741, 38211, 38983, 39787

Offset: 1

Alex Ratushnyak, Jul 05 2013

nonn

The sequence consists mainly of terms of A055574 = { n | sigma(n+1) = sigma(n-1) }. - M. F. Hasler, Aug 06 2015

			Sigma(8507) = 8736 divides sigma(8505) = 17472 = 8736*2, so 8506 is in the sequence.

Amiram Eldar, Table of n, a(n) for n = 1..6000 (term 1..280 from Harvey P. Dale)

Cf. A000203, A055574, A067130, A058073.

Flatten[Position[Partition[DivisorSigma[1,Range[40000]],3,1], ?(Divisible[ #[[1]],#[[3]]]&),{1},Heads->False]]+1 (* _Harvey P. Dale, Jul 15 2014 *)

A260988 Numbers n such that sigma(n) = m*sigma(n+2) with some m > 1.

Original entry on oeis.org

8505, 25500, 30360, 37740, 40740, 123795, 141480, 185460, 442365, 485400, 834435, 953568, 1055460, 1097820, 1108320, 1397220, 1953960, 2088480, 2208840, 2571744, 3050784, 3342816, 3544695, 3810456, 4314156, 4725660, 4867236, 5638776, 6318180, 6596340, 8428320, 8630832, 9347280, 9576336, 9908460, 10271580, 10992360, 11789925

Offset: 1

M. F. Hasler, Aug 06 2015

nonn

Sequence A227304 is the union of A055574 and { a(n)+1 }.

Many but not all terms are multiples of 5.

Cf. A000203, A055574, A067130, A058073.

for(n=1,2e9,sigma(n)%sigma(n+2)||sigma(n)==sigma(n+2)||print1(n","))

cp's OEIS Frontend

A227304 Numbers k such that sigma(k+1) divides sigma(k-1).

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