A074195 Sum of the primes from smallest prime factor of n to the largest prime factor of n = largest difference between consecutive divisors of n (ordered by size).

4, 20, 1278, 1339, 11074308238, 19096347067

Offset: 1

Author

Jason Earls, Sep 19 2002

Keywords

• more
• nonn

Comments

10^11 < a(7) <= 8912510129422438. - Giovanni Resta, May 13 2016

Crossrefs

Cf. A060681, A074036, A055233, A055514.

Programs

Mathematica

Select[Range[2, 2000], (p = First /@ FactorInteger[#]; #-#/p[[1]] == Sum[ Prime[i], {i, PrimePi@ p[[1]], PrimePi@ p[[-1]]}]) &] (* Giovanni Resta, May 13 2016 *)

PARI

isok(n) = {pf = factor(n)[,1]; my(pmin = vecmin(pf)); s = 0; forprime(p = pmin, vecmax(pf), s += p); s == n - n/pmin;} \\ Michel Marcus, Feb 03 2014

Extensions

a(5)-a(6) from Giovanni Resta, May 13 2016