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A254325 Sequence of semiprimes with all cumulating sums being semiprime. 1
4, 6, 15, 26, 55, 111, 237, 469, 926, 1858, 3711, 7419, 14849, 29693, 59435, 118821, 237722, 475378, 950738, 1901474, 3802967, 7605921, 15211942, 30423869, 60847667, 121695326, 243390743, 486781401, 973562795, 1947125641, 3894251303, 7788502531, 15577005118 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(1)=4, then a(n) is the least semiprime > a(n-1) such that a(1)+...+a(n) is semiprime.

LINKS

Zak Seidov, Table of n, a(n) for n = 1..89

EXAMPLE

4+6=10=2*5, 10+15=25=5*5, 25+26=51=3*17.

MATHEMATICA

s={4}; a=4; Do[m=a+1; While[2!=PrimeOmega[m]||2!=PrimeOmega[m+a], m++]; AppendTo[s, m]; a=m+a, {50}]; s

PROG

(PARI){s=[4]; a=4;

for(k=1, 50, m=a+1while(2<>bigomega(m)||2<>bigomega(m+a), m++);

s=concat(s, m); a=m+a); s}

CROSSREFS

Cf. A001358 (semiprimes), A065516.

Sequence in context: A027631 A128620 A045907 * A034299 A007135 A294070

Adjacent sequences:  A254322 A254323 A254324 * A254326 A254327 A254328

KEYWORD

nonn

AUTHOR

Zak Seidov, Feb 05 2015

STATUS

approved

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Last modified May 11 19:29 EDT 2021. Contains 343808 sequences. (Running on oeis4.)