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
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
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