A064019 Numbers k such that sopf(k) = sopf(k^2 - 1), where sopf(k) = A008472(k).

1, 5, 51, 99, 155, 209, 2369, 2569, 2882, 5745, 15143, 21691, 34573, 36566, 40516, 41237, 65304, 82718, 101638, 112305, 185701, 238302, 247221, 254865, 291399, 439104, 445794, 483107, 532645, 538531, 570020, 690238, 698561, 772485, 805013

Offset: 1

Author

Jason Earls, Sep 07 2001

Keywords

• nonn

Links

• Giovanni Resta, Table of n, a(n) for n = 1..1000 (first 100 terms from Harry J. Smith)

Programs

PARI

sopf(n,s,fac,i)=fac=factor(n); for(i=1,matsize(fac)[1],s=s+fac[i,1]); return(s);
for(n=1,10^6, if(sopf(n)==sopf(n^2-1),print(n)))

PARI

sopf(n)= { local(f,s=0); f=factor(n); for(i=1, matsize(f)[1], s+=f[i, 1]); return(s) }
{ n=0; for (m=1, 10^9, if (sopf(m)==sopf(m^2 - 1), write("b064019.txt", n++, " ", m); if (n==100, break)) ) } \\ Harry J. Smith, Sep 06 2009

Extensions

a(21)-a(35) from Donovan Johnson, Jun 15 2009