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A057230 Numbers n such that n=p+q=r+s with p*q=r*s=primorial number(A002110) (p*q)<(r*s). 0
31, 107, 391, 467, 34049, 67973, 176413 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The corresponding pairs of primorial are: (3#, 4#), (4#, 5#), (5#, 6#), (5#, 6#), (7#, 9#), (8#, 9#), (8#, 10#). No other terms found up to 23#. - Michel Marcus, Feb 21 2016

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

31 = 30+1 = 21+10, where 30=30*1 and 210=21*10 are primorial numbers.

PROG

(PARI) isprimo(n) = {if (n==1, return (1)); if (!issquarefree(n), return(0)); f = factor(n); #f~ == primepi(vecmax(f[, 1])); }

isok(n) = {c = 0; for (na=1, n\2, if (isprimo(na*(n - na)), c++); if (c == 2, return(1)); ); } \\ Michel Marcus, Feb 20 2016

CROSSREFS

Cf. A002110, A006862, A182987.

Sequence in context: A103069 A206526 A141877 * A225397 A142177 A281194

Adjacent sequences:  A057227 A057228 A057229 * A057231 A057232 A057233

KEYWORD

nonn,more

AUTHOR

Naohiro Nomoto, Sep 19 2000

STATUS

approved

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Last modified September 24 17:09 EDT 2020. Contains 337321 sequences. (Running on oeis4.)