login
A121976
Increasing sequence of odd primes such that abundancy(a(1)*...*a(n)) < 2, where abundancy(k) = A000203(k)/k. Generates "near perfect numbers".
0
3, 5, 7, 11, 389, 29959, 128194589, 566684450325197, 29753376105337343078941364947, 30082232218581187462432471034748868284388270918928732239
OFFSET
1,1
FORMULA
a(n) = nextprime(1 / (2 / abundancy(a(1) * ... * a(n-1)) - 1)) for n >= 4
EXAMPLE
a(5)=389 because abundancy(3*5*7*11*383) = 2.000013... > 2 and abundancy(3*5*7*11*389) = 1.999933... < 2.
PROG
(PARI) print(3); print(5); print(7); n=105; for(i=4, 7, k=nextprime(1 / (2 / abundancy(n) - 1)); print(k); );
CROSSREFS
Sequence in context: A245722 A262962 A321367 * A339789 A293598 A243179
KEYWORD
nonn
AUTHOR
STATUS
approved