A068365 Numbers k such that sigma(k) = phi((prime(k)+prime(k+1))/2).

14, 24, 308, 474, 690, 1242, 2970, 9690, 10340, 13110, 18270, 26400, 161880

Offset

1,1

Comments

Are there any odd numbers in the sequence?

There are no more terms up to 2500000. - Rick L. Shepherd, Aug 29 2002

No more terms below 3*10^9. - Amiram Eldar, Feb 01 2024

Links

Table of n, a(n) for n=1..13.

Mathematica

Select[Range[2, 162000], DivisorSigma[1, #]==EulerPhi[ (Prime[ #]+ Prime[ #+1])/2]&] (* Harvey P. Dale, Aug 23 2021 *)

Prog

(PARI) for(n=2, 2500000, if(sigma(n)==eulerphi((prime(n)+prime(n+1))/2), print1(n, ", ")))

Crossrefs

Cf. A000010, A000203.

Sequence in context: A211323 A141838 A140499 * A154038 A366960 A061923

Adjacent sequences: A068362 A068363 A068364 * A068366 A068367 A068368

Keyword

nonn,more

Author

Benoit Cloitre, Feb 28 2002

Extensions

More terms from Rick L. Shepherd, Aug 29 2002

Status

approved