

A253474


Numbers n such that the difference between n^2 and largest prime less than n^2 is not prime.


0



2, 11, 17, 23, 25, 31, 39, 41, 45, 51, 53, 56, 57, 59, 65, 67, 73, 76, 79, 81, 83, 85, 87, 91, 95, 97, 99, 100, 101, 105, 109, 111, 113, 115, 123, 125, 129, 133, 137, 141, 143, 147, 149, 151, 153, 154, 157, 159, 163, 165, 167, 170, 171, 175, 179, 181, 185, 187, 189, 193, 195, 197, 199, 201, 203, 207, 209, 213, 215, 219, 221, 225
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OFFSET

1,1


COMMENTS

Indices of terms in A056927 that are not prime.


LINKS

Table of n, a(n) for n=1..72.
Richard L. Francis, Between consecutive squares, Missouri Journal of Mathematical Sciences, Volume 16 Issue #1  Winter 2004.


EXAMPLE

a(1) = 2, since 2^2  3 = 1.
a(2) = 11, since 11^2  113 = 8.
a(3) = 17, since 17^2  283 = 6.
a(4) = 23, since 23^2  523 = 6.


MATHEMATICA

f[n_] := n^2  NextPrime[n^2, 1]; Select[Range[2, 230], !PrimeQ[f[#]] &]


PROG

(PARI) lista(nn) = for (n=2, nn, if (!isprime(n^2precprime(n^2)), print1(n, ", "))); \\ Michel Marcus, Mar 22 2015


CROSSREFS

Cf. A000040, A000290, A056927, A053001.
Sequence in context: A309499 A173638 A018420 * A133410 A156829 A255609
Adjacent sequences: A253471 A253472 A253473 * A253475 A253476 A253477


KEYWORD

nonn,easy


AUTHOR

Carlos Eduardo Olivieri, Mar 17 2015


STATUS

approved



