A107815 Primes p such that sigma(k) = phi(prime(k)-1), where p = prime(k).

2, 17, 67, 211, 631, 1051, 1811, 1951, 2287, 2791, 3331, 7297, 10099, 13597, 15739, 19717, 21169, 22153, 41341, 85933, 400051, 2251201, 2991253, 3051751, 4244791, 5713891

Offset

1,1

Comments

a(n) = prime(A067651(n)).

Values of k are in A067651, values of sigma(k) are in A107816.

Links

Table of n, a(n) for n=1..26.

Example

a(3) = prime(A067651(3)) = prime(19) = 67.

Mathematica

Prime[#]&/@Select[Range[400000], DivisorSigma[1, #]==EulerPhi[Prime[#]-1]&] (* Harvey P. Dale, Sep 01 2021 *)

Prog

(PARI) m=400000; for(n=1, m, p=prime(n); if(sigma(n)==eulerphi(p-1), print1(p, ", ")))

Crossrefs

Cf. A067651, A107816.

Sequence in context: A037420 A034721 A281708 * A042803 A182876 A056074

Adjacent sequences: A107812 A107813 A107814 * A107816 A107817 A107818

Keyword

nonn,more

Author

Klaus Brockhaus, May 24 2005

Status

approved