A121976 Increasing sequence of odd primes such that abundancy(a(1)*...*a(n)) < 2, where abundancy(k) = A000203(k)/k. Generates "near perfect numbers".

3, 5, 7, 11, 389, 29959, 128194589, 566684450325197, 29753376105337343078941364947, 30082232218581187462432471034748868284388270918928732239

Offset

1,1

Links

Table of n, a(n) for n=1..10.

Valeryi Kuryshev, NMBRTHRY Archives, 2006

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

Cf. A000396, A000203.

Sequence in context: A245722 A262962 A321367 * A339789 A293598 A243179

Adjacent sequences: A121973 A121974 A121975 * A121977 A121978 A121979

Keyword

nonn

Author

Charles R Greathouse IV, Sep 05 2006

Status

approved