A294906 a(n) is the least squarefree integer, product of n primes that are symmetrically distributed around their average.

2, 6, 105, 2145, 53295, 1616615, 57998985, 3038795305, 3907126810041, 7292509103495, 66240019730740785, 82246340873964085, 1870667082297874652055, 343515424581301546805, 9160656702012692171113335, 2356596317899272514936585, 1903895854998638367242867256645

Offset

1,1

Links

Table of n, a(n) for n=1..17.

Example

The prime factors of the first terms are: [2], [2, 3], [3, 5, 7], [3, 5, 11, 13], [3, 5, 11, 17, 19], [5, 7, 11, 13, 17, 19], [3, 5, 11, 17, 23, 29, 31], ...

Prog

(PARI) isok(n, nb) = {if (issquarefree(n) && (omega(n)==nb), f = factor(n)[, 1]~; avg = vecsum(f)/#f; for (k=1, #f\2, if (f[k] + f[#f-k+1] != 2*avg, return(0)); ); return (1); ); }
a(n) = {my(k = prod(i=1, n, prime(i))); while (! isok(k, n), k++); k; }

Crossrefs

Cf. A262723, A294751, A294752, A294776.

Sequence in context: A054247 A278888 A099790 * A284262 A287935 A357090

Adjacent sequences: A294903 A294904 A294905 * A294907 A294908 A294909

Keyword

nonn

Author

Michel Marcus, Nov 10 2017

Extensions

a(8)-a(17) from Giovanni Resta, Nov 10 2017

Status

approved