OFFSET

1,1

COMMENTS

All the terms are even.

Includes all the numbers of the form p+1 where p is an odd prime (A008864 \ {3}).

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

D. R. Heath-Brown, Cheryl E. Praeger and Aner Shalev, Permutation groups, simple groups, and sieve methods, Isr. J. Math., Vol. 148 (2005), pp. 347-375; alternative link.

FORMULA

The number of terms that do not exceed x is N(x) = h * x/log(x) + O(x/log(x)^2), where h = A370746.

MATHEMATICA

q[n_] := AnyTrue[Divisors[n], PrimeQ[n/# - 1] && Divisible[n/# - 2, 2*#] &]; Select[Range[250], q]

PROG

(PARI) is(n) = {my(d = divisors(n)); for(i=1, #d, if(isprime(n/d[i]-1) && !((n/d[i]-2) % (2*d[i])), return(1))); 0; }

CROSSREFS

KEYWORD

nonn,easy

AUTHOR

Amiram Eldar, Feb 29 2024

STATUS

approved