A365222 - OEIS

A365222

a(n) is the least semiprime such that a(n) - n and a(n) + n are the previous and the next semiprimes.

34, 185, 262, 407, 314, 371, 194, 2271, 6218, 4237, 109898, 110645, 53602, 169773, 112298, 163985, 284738, 48529, 1033378, 1781833, 570502, 1963091, 12527458, 6051613, 30377422, 19549343, 66761746, 7926901, 363311378, 5861227, 676386278, 136503631, 72622874, 51204973, 375025874

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..35.

EXAMPLE

a(3) = 262 because 262 = 2 * 131 is a semiprime, the previous semiprime is 262 - 3 = 259 = 7 * 37, the next semiprime is 262 + 3 = 265 = 5 * 53, and no semiprime less than 262 works.

MAPLE

N:= 46: # for a(1) .. a(N)

V:= Vector(N):

b:= 6: d:= 2: count:= 0:

for i from 7 while count < N do

if numtheory:-bigomega(i) = 2 then

ib:= i-b;

if ib = d and ib <= N then

if V[d] = 0 then V[d]:= b; count:= count+1 fi

else d:= ib

fi;

b:= i;