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A272862 Positive integers j such that prime(i) + prime(j) = i*j for some i <= j. 3
4, 6, 8, 24, 29, 30, 164, 165, 166, 1051, 2624, 2638, 2650, 2670, 2674, 2676, 40027, 40028, 40112, 251701, 251703, 251706, 251751, 637144, 637202, 637216, 637220, 1617162, 1617165, 4124694, 10553383, 10553408, 10553464, 10553533, 10553535, 10553839, 69709686 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also pi(q) for primes q verifying p+q = pi(p)*pi(q) for some prime p <= q.

The list of products i*j gives A272860. See also comments there.

LINKS

Giuseppe Coppoletta, Table of n, a(n) for n = 1..43

EXAMPLE

8 is a term as prime(3) + prime(8) = 3*8.

MATHEMATICA

Select[Range[3000], Function[j, Total@ Boole@ Map[Prime@ # + Prime@ j == # j &, Range@ j] > 0]] (* Michael De Vlieger, Jul 28 2016 *)

PROG

(Sage) def sol(n):

    if n<5: a=n

    else: a=exp(n+1)/(n+1)

    b=(n-1)/n^2*exp(n^2/(n-1.1))

    return [j for j in range(a, b) if is_prime(n*j-nth_prime(n)) and prime_pi(n*j-nth_prime(n))==j]

flatten([sol(i) for i in (1..15) if len(sol(i))>0]) #

(PARI) is(n) = for(i=1, n, if(prime(i)+prime(n)==i*n, return(1))); return(0) \\ Felix Fröhlich, Jul 27 2016

(PARI) is(n, p=prime(n))=my(i); forprime(q=2, p, if(i++*n==p+q, return(1))); 0

v=List(); n=0; forprime(p=2, 1e6, if(is(n++, p), listput(v, n))); Vec(v) \\ Charles R Greathouse IV, Jul 28 2016

CROSSREFS

Cf. A272860, A272861, A000720, A000040.

Sequence in context: A217201 A074125 A063719 * A106366 A019160 A126233

Adjacent sequences:  A272859 A272860 A272861 * A272863 A272864 A272865

KEYWORD

nonn

AUTHOR

Giuseppe Coppoletta, Jul 25 2016

STATUS

approved

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Last modified January 27 14:39 EST 2020. Contains 331295 sequences. (Running on oeis4.)