21171

Appears in sequences

• Decimal encoding of the prime factorization of n: concatenation of prime factors and exponents.at n=32A067599
• a(1) = 11 by convention; for n > 1, if n = p^a*q^b... then a(n) = concatenate(p,a,q,b,...).at n=33A068633
• Numbers k such that k and k^2 use only the digits 1, 2, 4, 7 and 8.at n=27A136997
• Number of compositions of n with at most one 1.at n=20A206268
• Least integer k such that the n-th prime of form m^2+1 divides the composite number k^2+1.at n=26A255675
• Number of nX2 0..1 arrays with no element equal to more than three of its king-move neighbors, with the exception of exactly two elements, and with new values introduced in order 0 sequentially upwards.at n=8A281159
• T(n,k)=Number of nXk 0..1 arrays with no element equal to more than three of its king-move neighbors, with the exception of exactly two elements, and with new values introduced in order 0 sequentially upwards.at n=46A281165
• Semiprimes m = p*q where m, p and q are in A033638 (locations of right angle turns in Ulam square spiral).at n=10A331997