27971

Appears in sequences

• Discriminants of totally complex sextic fields (negated).at n=25A023687
• All 81 combinations of prefixing and following a(n) by a single digit are nonprime.at n=13A032734
• a(n) cannot be prefixed or followed by any digit to form a prime ('empty' prefixes allowed).at n=1A032736
• Composite numbers k such that all the decimal concatenations ik and ikj (i, j = 1...9) are also composite.at n=7A032737
• a(n) cannot be prefixed or followed by any digit to form a prime ('empty' prefixes and suffixes are allowed).at n=1A032738
• Number of n-node rooted identity trees of height 6.at n=13A038090
• Pell pseudoprimes: odd composite numbers n such that P(n)-Kronecker(2,n) is divisible by n.at n=30A099011
• Number of peaks at odd level in all Dyck paths of semilength n that have no ascents and no descents of length 1.at n=15A167636
• Expansion of exp( Sum_{n >= 1} A188458(n)*x^n/n ).at n=8A188514
• Extra strong Lucas pseudoprimes.at n=4A217719
• Integers n such that n!/(n-2) + 1 is prime.at n=32A271376
• Composite numbers k such that Pell(k) == -1 (mod k).at n=4A319043
• Composite numbers k coprime to 8 such that k divides Pell(k - Kronecker(8,k)), Pell = A000129.at n=44A327651
• Intersection of A099011 and A327651.at n=17A327652
• NSW pseudoprimes: odd composite numbers k such that A002315((k-1)/2) == 1 (mod k).at n=21A330276