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A131368 Coprime semiprimes: a(n-1) and a(n) are the closest coprime semiprimes. 2
4, 9, 10, 21, 22, 25, 26, 33, 34, 35, 38, 39, 46, 49, 51, 55, 57, 58, 65, 69, 74, 77, 82, 85, 86, 87, 91, 93, 94, 95, 106, 111, 115, 118, 119, 121, 122, 123, 133, 134, 141, 142, 143, 145, 146, 155, 158, 159, 161, 166, 169, 177, 178, 183, 185, 187, 194, 201, 202, 203 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The slowest increasing sequence of semiprimes with coprime neighbor terms.

LINKS

Table of n, a(n) for n=1..60.

FORMULA

gcd(a(n-1),a(n))=1.

PROG

(PARI) lista(nn) = {my(vsp = select((x->(bigomega(x) == 2)), vector(nn, k, k)), i = 1, last); while (i <= #vsp, print1(vsp[i], ", "); last = vsp[i]; while(gcd(vsp[i], last) != 1, i++; if (i>#vsp, break)); ); } \\ Michel Marcus, Jun 25 2019

CROSSREFS

Cf. A051884, A061766, A107621, A109412.

Subsequence of A131368 (semiprimes).

Sequence in context: A119718 A263648 A051884 * A131457 A072525 A107621

Adjacent sequences:  A131365 A131366 A131367 * A131369 A131370 A131371

KEYWORD

nonn

AUTHOR

Zak Seidov, Sep 30 2007

STATUS

approved

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Last modified November 13 17:34 EST 2019. Contains 329106 sequences. (Running on oeis4.)