A211660 Numbers k such that k and k+2 both have unique values of sigma(k) and sigma(k+2); sigma(k) = A000203(k) = sum of divisors of k.

1, 2, 3, 5, 7, 27, 43, 98, 146, 169, 171, 197, 200, 217, 241, 257, 281, 331, 347, 379, 386, 409, 448, 461, 487, 505, 507, 509, 547, 554, 576, 577, 641, 800, 821, 829, 841, 857, 907, 937, 1117, 1250, 1261, 1283, 1289, 1322, 1352, 1359, 1387, 1415, 1601, 1621

Offset

1,2

Comments

Subsequence of A211656. Number k is in sequence iff k and k+2 are in A211656.

Supersequence of A211767 (lesser of twin primes p, p+2 with unique values of sigma(p) and sigma(p+2)).

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

Number 27 is in sequence because sigma(27) = 40, sigma(29) = 30 and there are no other numbers m, n with sigma(m) = 40 or sigma(n) = 30.

Crossrefs

Cf. A000203, A211656, A211657, A211658, A211659, A211767, A211768, A211769.

Sequence in context: A333955 A333960 A273726 * A215155 A228486 A117135

Adjacent sequences: A211657 A211658 A211659 * A211661 A211662 A211663

Keyword

nonn

Author

Jaroslav Krizek, Apr 20 2012

Status

approved