A254325 Sequence of semiprimes with all cumulating sums being semiprime.

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

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: A128620 A358438 A045907 * A351145 A034299 A007135

Adjacent sequences: A254322 A254323 A254324 * A254326 A254327 A254328

Keyword

nonn

Author

Zak Seidov, Feb 05 2015

Status

approved