A260420 Numbers n such that sigma(n+1) - sigma(n-1) = n+1.

2, 3, 23, 14927, 31049, 69107, 246263, 5860169, 307164671, 881198663, 1489455647, 2386555631, 8225563703, 14311679063, 111494234183, 154357775303, 299004519623, 870455062823, 970388922263, 991817878343, 1677028870823, 1782783762503, 1830446935223

Offset

1,1

Comments

Proposed by Jaroslav Krizek in A260071.

Also: numbers n such that A001065(n+1) = A000203(n-1).

Links

Giovanni Resta, Table of n, a(n) for n = 1..33 (terms < 10^13)

Formula

a(n) = A246852(n) + 1.

Mathematica

Select[Range@ 1000000, DivisorSigma[1, # + 1] - DivisorSigma[1, # - 1] == # + 1 &] (* Michael De Vlieger, Jul 25 2015 *)

Prog

(PARI) for(n=2, 1e9, sigma(n+1)-sigma(n-1)==n+1&&print1(n", "))
(Magma) [n: n in [2..5*10^6] | DivisorSigma(1, n+1) - DivisorSigma(1, n-1) eq n+1]; // Vincenzo Librandi, Jul 26 2015

Crossrefs

Cf. A260071, A076530, A246852.

Sequence in context: A360225 A238265 A203015 * A241661 A260071 A115031

Adjacent sequences: A260417 A260418 A260419 * A260421 A260422 A260423

Keyword

nonn

Author

M. F. Hasler, Jul 25 2015

Status

approved