OFFSET
1,2
COMMENTS
The first 131072 terms of this sequence are even. Conjecturally, all terms are even.
Numbers in the range of the sum of perfect divisors function (A187794). - Timothy L. Tiffin, Jul 13 2016
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
502 = 496 + 6, where 496 and 6 are perfect.
MATHEMATICA
With[{perf = Select[Range[10000], DivisorSigma[1, #] == 2# &]}, Rest[Union[Total/@Subsets[perf]]]] (* Harvey P. Dale, Feb 07 2012 *)
PROG
(PARI) vecsum(v)=sum(i=1, #v, v[i]);
v=apply(n->binomial(n+1, 2), select(k->ispseudoprime(k), vector(15, n, 2^prime(n)-1))); u=List(); for(i=0, 2^#v-1, listput(u, vecsum(vecextract(v, i)))); vecsort(Vec(u)) \\ Charles R Greathouse IV, Feb 09 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Charles R Greathouse IV, Feb 09 2012
STATUS
approved