|
|
A064439
|
|
Numbers n such that sigma(n) - n - 1 = pi(n).
|
|
0
|
|
|
4, 55, 65, 95, 125, 145, 155, 185, 205, 2779, 2863, 55297, 174691, 174779, 487903, 1301989, 1302457, 5254751, 6383483, 23140961, 48267437, 59651051, 70111213, 70111247, 92514491, 199445641, 212210443, 514269523, 514269599, 21881358361, 1602278990111
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
|
|
LINKS
|
|
|
MATHEMATICA
|
Select[Range[10^5], DivisorSigma[1, #] - # - 1 == PrimePi[#] &] (* Giovanni Resta, Mar 31 2017 *)
|
|
PROG
|
(PARI) sig(n) = sigma(n)-n-1; pi(x, c=0) = forprime(p=2, x, c++); c for(n=1, 10^8, if(sig(n)==pi(n), print(n)))
(PARI) { n=0; for (m=1, 10^9, if ((sigma(m) - m - 1)==primepi(m), write("b064439.txt", n++, " ", m); if (n==100, break)) ) } \\ Harry J. Smith, Sep 14 2009
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|