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A374055
a(1)=1, a(2)=4, and thereafter a(n) = a(n-2) + k * a(n-1), with minimal k >= 1 such that a(n) is not prime.
0
1, 4, 9, 22, 75, 172, 247, 666, 913, 2492, 3405, 9302, 12707, 22009, 34716, 56725, 91441, 148166, 239607, 387773, 627380, 1015153, 1642533, 2657686, 4300219, 6957905, 11258124, 18216029, 29474153, 47690182, 77164335, 124854517, 202018852, 326873369, 528892221
OFFSET
1,2
EXAMPLE
For n=5, the smallest 9 + k*22 which is not prime is a(5) = 75 at k=3.
CROSSREFS
Sequence in context: A231338 A257272 A370021 * A070713 A060250 A138991
KEYWORD
nonn
AUTHOR
STATUS
approved