A222174 Numbers n such that sigma(n) + sigma(n-1) = 3n, where sigma(n) = sum of divisors of n (A000203).

6, 34, 50, 236, 262, 386, 898, 8362, 26938, 46594, 80876, 5244548, 5462384, 17062316, 323987588, 1162300834, 1381439876

Offset

1,1

Comments

34 is the only number < 10^10 such that sigma(n) + sigma(n+1) = sigma(n) + sigma(n-1) = 3n (34 is a term of A067806).

a(16) > 5*10^8. - Giovanni Resta, May 13 2013

a(18) > 10^10. - Donovan Johnson, May 13 2013

Links

Table of n, a(n) for n=1..17.

Mathematica

For[n=1, True, n++, If[DivisorSigma[1, n]+DivisorSigma[1, n-1]==3n, Print[n]]]

Prog

(PARI) is(n)=sigma(n)+sigma(n-1)==3*n \\ Charles R Greathouse IV, May 13 2013

Crossrefs

Cf. A067806 (numbers n such that sigma(n) + sigma(n+1) = 3n), A000203.

Sequence in context: A375569 A190644 A011798 * A044464 A113528 A152528

Adjacent sequences: A222171 A222172 A222173 * A222175 A222176 A222177

Keyword

nonn

Author

Jaroslav Krizek, May 13 2013

Extensions

a(12)-a(15) from Giovanni Resta, May 13 2013

a(16)-a(17) from Donovan Johnson, May 13 2013

Status

approved